350-400W is plenty. The best way to check is to go to intel's web site and see what power supplies are recommended with your particular CPU. Make sure the 5 VSB is rated at least 1.5A or you will have trouble with ACPI if you board is so equipped.
Dear god, do yourself a favor and upgrade to 256Mb Rdram, you will see a huge increase over 128mb. Don't forget, you have to get pairs of rdr, they work in a dual channel configuartion. Yes, an enermax 350 watts is sufficient. Looks good.