Hi, sorry if this isn't the best place to put this.

I am currently looking to upgrade my system (mainly the motherboard and video card), but I'm on a bit of a budget and I need some help deciding what would be best to get and what is compatible with what.
I am mainly doing this because my graphics card is starting to go and I was told that if I want to upgrade my video card, I should go with PCI_Express, but my motherboard does not suppport it.

I mainly like to play First Person Shooters (not necessarily to their fullest graphical potential), RTS and WoW

My friend helped me build this system a few years ago, so I don't know exactly what I am doing.
So, any feedback would be much appreciated

Here is a summary of my PC details (pulled using Belarc Advisor)
If you need any more info, just let me know and I will try to get it

Thanks =)

Processor:
2.80 gigahertz Intel Pentium 4
8 kilobyte primary memory cache
512 kilobyte secondary memory cache

Main Circuit Board:
Board: ASUSTeK Computer Inc. P4P800SE Rev 2.xx
Bus Clock: 200 megahertz
BIOS: American Megatrends Inc. 080009 03/15/2004

Memory Modules:
024 Megabytes Installed Memory

Slot 'DIMM0' has 512 MB
Slot 'DIMM1' is Empty
Slot 'DIMM2' has 512 MB
Slot 'DIMM3' is Empty

Power Supply:
Wattage: 300W
Model Number: AP-350X

Display:
NVIDIA GeForce FX 5500 [Display adapter]
Samsung SyncMaster [Monitor] (19.1"vis, s/n H9NLC05448, December 2006)

Can you change out your power supply? I'd recommend you do this first before changing video cards. A 400w fortron fsp will run you about $45 shipped. With this ps, you can run an average video card, such as the 2600 pro or 7600gs. The 2600 will give you directx10 support if you plan on using vista. If you don't care about vista, then an older card such as the 7600 will work fine. Newegg has hundreds of video card listings, several with rebates. I use antec power supplies; newegg has a 380w and 500w earthwatts model(s) with rebates, if you want to use one of these.

Thanks for the response =)
Do you have any recommendations on a decent motherboard that supports pci-e that is relatively inexpensive?

On a side note, would it be the power supply causing my system to shut off whenever I use my DVD burner for anything? (my DVD Rom works fine without this issue) if so, I would need to replace it anyways.