At such a low budget, Dell might be the way to go. But it's still possible to build a better computer at that budget, giving a little more cash into it, because the parts will be of higher quality than Dell's.
Here's a quick list I pulled up, costing less than $400, without a monitor. No shipping included:
Case - Rosewill R5604-BK Mid Tower
Processor - Intel Pentium Dual Core Allendale E2160 1.8GHz
Motherboard - Gigabyte P31-S3G
Memory - 2 x 1GB DDR2-800 NQ
Graphics cards - EVGA 8600GT 256MB 128-bit
Power supply - Rosewill RP500-2 500W
You can use your current hard drive and optical drive, with that list too.