My advice is figure out how much your willing to spend first then buy the parts yourself...
trust me some Lego projects are more difficult than putting a PC together..
You don't have to go super high-end...
even middle of the road is fine...
try and get a solid state drive for you OS... if nothing else this will make a big difference
I build my own with the parts "I Want" not what they think is best. Mainstream Computers are overpriced pieces of junk. The big thing is to have a Power Supply with enough Watts (Voltage x Amps) for the parts to work at maximum efficiency. Nothing is worse than underpowered innards.
Compare your game requirements with your budget and preferred form factor, then go from there
A half decent gaming rig at the current level will run you between $1,500.00 and $2,000.00 with a good video card and plenty of RAM. Don't waste a lot of money on an expensive sound system unless you are getting a 7.1 surround set up with speakers made for it. A good pair of surround headphones works wonders with a middle of the road card.
depends on the game you want to run. state of the art that can play all the newest games at max resolution? like $3k.
something that will play most things well? maybe $1000
the biggest thing you want is: ram (lots and lots of ram) and a great video card. top of the line can run you like $300. i would buy it seperatly though and install it yourself. itll be cheaper.
Laptops can be upgraded. You just really need to know what you are doing. If you want to be able to run the latest games at their highest quilaty, that can cost up to 3k. If you are willing to settle for min, then still probably around $700 min to be able to run the latest games. Unless you know how to build your own comp. Then it can be as cheap as $200. So highly variable.
I got mines costumed built. Ordered most of the parts off Newegg.com :)
About $350.00 (US) can get you a decent Dell desktop computer.
Cnet's the best place to go.(google)