what psu....

Should I have if I'm running:
AM2 64X2 4800+ 2.5 HGz
MSI K9A2 Platinum
2gb G. Skill
XFX 5750

i have a 450w now and feel like I am barely getting by.

well.. assuming 1 hdd, and one optical drive... about a 400... if you have 2 hdds then a 500 or 550 watt

newegg recommends at least 370w with your build, 500w seems pretty much the standard.

According to THIS CALCULATOR you don't even need 300w and the recommended is 341w so your 450 is plenty. You should bear in mind though that PSU's lose capacity with age - some people say you should assume a 10% power loss for each year of use although I can't personally vouch for that.

My main rig is running on a 450w coolermaster with a power meter. Intel Quad core 2.75, 8GB ram, 4870 graphics, 2 hard disks and 1 optical, and it is more than ample.... Don't assume you need a mega PSU unless you're doing some serious overlocking and running non-standard items like screens, displays, watercooling pumps etc....

/\ What slave said. With those specs, 450W will be more than enough, even taking aging into account, as long as you have a well made (~80%+ efficiency) PSU. OOC, what makes you think you don't have enough power?