Well, you probably don't want to hear this...but here goes:
The case you have is possibly not going to accommodate an industry standard motherboard.
So you are looking at buying a motherboard, and probably a case, and likely RAM...at minimum.
Those three things can be very inexpensive...or very expensive depending on what you want.
You are in kind of tough spot with that CPU because it sits in a socket that is dead technology.
But here is my advice:
Option 1 - The more expensive alternative.
Buy a new motherboard, below are some suggestions that will not kill you financially, that are solid boards, and are going to be upgradable down the line.
#1 - Foxconn X38A LGA 775 Intel X38 ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E16813186134
Why?
It's less than $150 with rebate, it is a very solid board with tons of features, it's an Intel chipset with 2 PCIe slots for SLI/Crossfire, and most importantly, it supports DDR2
or DDR3 RAM.
I built a machine for someone using this board recently and she loves it!
#2 ASRock X38TurboTwins LGA 775 Intel X38 ATX
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157136R
Why?
It's cheap. And it has 2 PCIe slots and supports both DDR2 and DDR3. I have not dealt with this board in the past, so I cannot vouch for it.
With either of these boards, you are going to need to buy new RAM unfortunately as well. But the good news is, DDR2 800 is almost free these days
Shop around at like
www.newegg.com,
www.tigerdirect.com, etc...and you can usually get 2GB of DDR2 800 for like $20.
Later, when the cost comes down, you can throw in DDR3 RAM and get an instant upgrade without pulling your mobo and reinstalling Windows and all that fun stuff.
Going this route you will need a new CPU.
Right now, for cost vs. performance...I recommend:
Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115037
Why?
It's not terribly expensive, it runs at 3 Ghz, it's dual core, and it has a 6MB cache as opposed to 2 or 4 MB on some other processors. The 65W draw is nice too because it runs cooler than some other CPUs out there (prolongs life of CPU).
Finally...
You will need a video card.
Right now, I recommend:
POWERCOLOR AX3870 512MD3-PH Radeon HD 3870 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card
http://www.newegg.com/Product/Produ...10380048 106792462&name=Radeon HD 3000 series
Or really any variation/brand of this card that strikes your fancy.
Why?
It's cheap...and it performs really, really, well.
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Now I am not sure what your power supply is like, but you will need to make sure it has a PCIe rail, or you may need to replace it. Also, 450 Watts is a little low, so if you do replace it...go at least 650.
As for a case...they are all basically the same. The differences are more features (USB ports, LED lights, number of case fans, size), looks (cool widgets, and LED panels, etc.), but there is some difference in construction to consider. Cheap cases tend to rattle more, and they can have sharp edges on the inside...so be careful (OUCH!). Generally, I think you are spending too much on a case if you drop more than about $70 on it. Granted, you can spend much more than that...but you don't need to.
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Option 2 - The cheaper way
You are running a P4 single core now...right?
You probably are not going to want to remain on that architecture for too much longer, but you
might be able to stay on a socket 478 CPU until the prices of the new 1366s come down to affordable levels.
If you want to reuse your RAM, it looks like you are running PC2100...so you will need a board that supports socket 478 and PC2100 RAM. I would go ahead and go with PCIe instead of AGP unless you just have an AGP card lying around collecting dust.
It's should be only like $60.00 or so...and you can drop your existing CPU and RAM into it. Just get a new case and a new video card (I still recommend the 3870 for PCIe ... or the 3850 AGP) and you should be all set.
You may have to go with something that is AGP with that RAM though. Most of the PCIe boards out there use 240pin RAM, you have 184pin.
After everything, you can do this for less than $200...if you get an inexpensive case and your 450W PSU has a PCIe rail. (you can also adapt a Molex rail on your PSU to PCIe with a $4 adaptor BTW and it won't matter if you have to go, or choose to go, AGP.)
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But here is something to be aware of.
You are likely going to have to format your hard drive and re-install Windows
Anytime you do a motherboard swap, it is not only advisable to do this...it is sometimes unavoidable.
Windows, when it was first installed on your system, has already allocated resources (addresses, interrupts, etc.) to your motherboard components (HD controller, PCI bridge, USB controller, etc. etc.). When you throw a new mobo in, and boot into Windows, assuming it will boot, it will need to find and reallocate all of those resources. This can often times create conflicts, which may cause performance degradation, or even failure.
It is my opinion that you are better off backing up any necessary files that you want to keep, and just getting a fresh, clean, installation of Windows whenever you swap mobos. Some people don't do this...but they should.
I hope some of this helps.
