Is 305 Watts enough ?

Use extreme PSU calculator (do a Google)

under 290w when I plug-n-chug, so it is probably ok unless it is a generic $20 type of psu that is bundled with most cases, in which case a 350+ "el cheapo" should be ok - assuming you have a non-accellerated card like Matrox g550.

Are you looking at a powerful gaming card like the X1900XTX, or something more for graphics like Matrox? Perhaps a budget ATI or nVidia GPU?

A video card can consume any where from 35w to 135w under full load. Therefore, it is difficult to recommmend a PSU if you do not provide all your specs.

don't forget that a no-name PSU don't put out as many W as it says, so there can be less than 305W

Here is my estimate of your power requirements @ 100% load:

P4 3.0GHz................................135w
Motherboard..............................20w
2 250GB HDDs..........................40w
2 DVD Drives.............................30w
2 Sticks of RAM.........................10w
2 Case Fans.............................10w
ATI X600..................................33w

Total Wattage @ 100% Load......278w
Typical gaming wattage............244w

I think that is cutting it close for a 305w PSU.

I recommend upgrading the PSU:

XClio 450BL 450W PSU = $40 - $4 Instant savings + $6 Shipping = $42

Here's a hardware review of it.

I would normally recommend a Seasonic S12 PSU since they are up to 85% efficient, quiet, and reliable, but the 380w version is slightly more than double the the cost of the XClio, and I assume you are on a budget.

Jesus everythink is nice in your setup but the PSU! a little bit more power like 450 or 500w wont kill you, what if in the future you need more HD space? You decide to chuck in a tv tuner more RAM etc? The extra 50 wats or so wont hrut its not like its going to consume more power and make your bills go up.