anything is possible, firts thought i would advice making a more personal subject as "computer" is very vauge and therefore people may not read this thread.
all you need for a computer to be functional is this.
-ram (prlly over 256mb and even more to play games)
-hard drive (around 80gb to play games you could get away with 40 or even 20 but 80 is about what you should have)
-video card (can be very expensive if you want to play high graphics games like HL2 or battle field or even Sims 2)
-Monitor (slef explainitory but i hate to say these cost about 150-thousands of dollars, you could get one for 120$ but again if you are intereested in playing games you are not going to want to go the cheep route)
-Power supply (this when pcik should come last they aren't expensive but if 300$ is your budget they might be, some cases come with power supplies (or PSU's) so also lok out for that
-CPU or central processing unit (these are small but it is basicly the computer you need one and for games you prlly want 3400+ or 3200+ but they do get expensive)
-speakers (personal prefence)
-*sound card (may already be on the motherboard)
-lasstly a case to put all the above goodies into...
in realality you prlly wnot be able to BUILD a comptuer for 300 (even with tax and warrenties which i suggest). but you could prlly by an inexpensive package from dell or somtihing that is around 500-ish.
to see the computer parts prices and get and idea for what you need. the above i mentioned is what you need but you dont have to get those speifications. but what ever you do be sure to post here first andj verify if its a good deal people here are very nice and helpful. i hhoped this helped a little.
ASUS A8V-E Deluxe | AMD Athlon 64 3800+ | Crucial 1GB 184-Pin DDR SDRAM (x2)
eVGA Geforce 7800GTX 256-P2-N528-AX Video Card
Saitek Black Wired | Logitech MX518 | Logitech THX Z-5300e 5.1 | ASPIRE X-Plorer ATXB8KLW-BK Black
ViewSonic VA912b Black 19" 20ms | SONY Black IDE CD-ROM | SONY Black IDE DVD Burner | SONY Black Internal Floppy Drive | SAMSUNG SpinPoint P Series 160GB (x2)[RAID 0]
neotech power supply 480watt
blue case fans :-)