I read somewhere that you are no longer getting a new machine. I wondered if this was due to cost, you had mentioned $600. Here is what I could put together for a bit cheaper than that, hopefully it will give you some room to negotiate.
I would like to see you commenting on beta for yourself

Its not a super PC or anything but it will do. I got a standard Power Supply nothing fancy but not super cheap because I feel its an item you shouldn't chinse on.
Intel Core 2 Duo E6300 Conroe 1.86GHz LGA 775 Processor Model BX80557E6300 - Retail
$181.00
ECS PT890T-A V1.0 LGA 775 VIA PT890 ATX Intel Motherboard - Retail
52.99
Kingston ValueRAM 512MB 240-Pin DDR2 SDRAM DDR2 533 (PC2 4200) System Memory Model KVR533D2N4/512 - Retail
31.99 x2 = 63.98
PNY VCG7300SXPB GeForce 7300GS 256MB GDDR2 PCI Express x16 Low Profile Video Card - Retail
65.99
Cooler Master RC-330-KKN1-GP ATX Computer CasesView Pic COOLER MASTER RC-330-KKN1-GP Black SECC ATX Mid Tower Computer Case - Retail
39.99
COOLER MASTER eXtreme RP-500-PCAR ATX from factor 12V V2.01 500W Power Supply - Retail
$49.99
TOTAL:453.94
All items were found on NewEgg and shipping should run you $30 - 40 dollars. If you can't get your parents to buy it maybe you should tap into your capitalistic nature and make some $

. If your friend can build it he might be able to overclock it for you, that chip is very OC able though that isn't the best mobo for that, it will do.
Good Luck, hope to see you in the game when Multiplayer Beta starts.