If your really serious about investing money into a computer this is what I suggest.
CPU: Latest Intel cpu with 1333 fsb
RAM 2GB DDR2 Ram, Windows XP can only benefit from a maximum of 2gb of ram unless you go with the 64bit edition
If you have Vista Ultimate, I say load it up! Vista supports more ram then Windows XP and is power hungry as heck, go for 4gb depending on the motherboard you select
Video: Go for SLI DX10 video cards, Though Guildwars will not truly benefit from SLI graphics or DX10, just about every other new game out there willl
I just love NVIDIA when it comes to graphics, their high end graphic boards cant be beat.
I recommend getting two Geforce 8800GTS 640mb DDR3 cards from either EVGA or XFX, they make the best cards. The plus about the 8800GTS over the 8800GTX is that it can be overclocked to the same spead or dang well near to the GTX
The Ultra or Ultra Superclocked are overkill unless you just want to go for it (I have 2x EVGA 8800Ultra 768mb cards

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Motherboard: Find the best there is and buy cheap parts around it if necessary. Easy to upgrade hardware, Hard and often limiting to change the motherboard once its had a few years and you want to keep all your original hardware
*Note: Take a moment and write down on paper everything you wish to do and everything you POSSIBLY will want to do in the future and build a system around that. it will save you alot of problems
Power: Things to take into consideration
- Numbers of cores your cpu will have, most likely 2 or 4 cores
- Number of video cards. this will double both the heat and power consumption
- power concumption of video cards. these things now consume more power then a power plant!
- Number of Rails
*Note: It is MUCH better to get a Quality Single Rail power supply. Do NOT get a cheap power supply.
Single Rail power supplies are MUCH better then dual rails
Cooling: Stock cooling for newer Intel products are often good but I always opt for better cooling through the form of a better CPU heatsink, etc.
Case: VERY IMPORTANT!!!!
This may sound trivial but your case will make a BIG difference.
Your computer case will determine various factors:
- Temperature: if your case is cramped and you have hot components, there wont be much room for airflow
- Ports: if you like ports on the front or not
- Screws or Screwless: Screwless is nice and helps not damage your hard drives and such and makes for easier access, but costs more money
- Weight: if you move your case often or go to LAN parties
- Capacity: how much stuff you can actually get in it
- Clearance: High end video cards can now be up to 11 inches long. Graphical ports are often located at the bottom of the motherboard and installing a large video card may actually cause clearance issues with your Hard Drive cage, rubbing against your hard drives or physically not fitting