| If you are not comfortable building the PC yourself, I would definitly not recommend it. While it's not really hard, there are still enough pitfalls.
I generally think it's the best way to let some retailer build your PC with handpicked components, as long as they give decent warranty.
I would never buy a PC from one of those major companies. I really don't see any advantage there, it just costs more.
For my own PC, I just go to a PC store here (there are plenty around), which offer this kind of service and it costs very little (~25) to have it put together including preinstalling OS with a 2-year warranty on the whole system on top.
I'm not sure what options in this direction you have, but I'm reasonably sure there are online retailers that should offer this kind of service and are perfectly reliable.
As for what components you should look out for, that depends on what you want to do with it...
Bye
Thanee
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In Memoriam Dave Arneson ( April 7th, 2009) & Gary Gygax ( March 4th, 2008). Wondering what the Dungeon Tiles are like? Take a look here (up to DU5 Sinister Woods). | 
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