I have an Antec True Power 330 that came in my case.

By the time I am done, I will have the following in my system:

MSI 6565 (GMB MAX-FISR)

Intel Celeron 3.06GHz (Hyper Threading enabled)

2x 512MB Corsair 333Mhz CAS 2 RAM

2x Maxtor Atlas IV 36GB U320 10K, I might leave my IBM Deskstar GXP-120 (80GB model) in the system...

Memorex 52X CD-RW

Creative Labs SB Live 5.1

M-Audio Delta 44 (dedicated Audio card for recording)

LSI Logic MegaRAID Express 500

4 case fans (2 front, one side, one back)

I think 330w would be cutting it close, but a 550w is too extreme. I think there is a 430w and 480w model as well.
Amazing how much difference a power supply can make when it comes to system instability.

Which one?