Which card for new monitor?

[chedderslam1]

I had a little extra money so I have treated myself to the dell ultrasharp 24" monitor. In my aging system, I have been using the integrated graphics for my little 17" monitor, but I would like to invest in a graphics card to get the most out of my monitor. The system has an agp slot, so it looks like I am limited to that.

I am considering this card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102730

I am concerned if my power supply can handle it, though. The power supply is a Enermax EG465P-VE, which I believe is rated to over 400 watts. Can that handle a 3850?

The system has a 2.4 P4 and 2 gigs of ram. I know I won't be able to play the latest games or anything, but will I be able to play older stuff at the monitor's native resolution? Really, my biggest concern is video playback as most hd streamed video maxes the processor and gets so choppy that it is unwatchable. I am hoping the graphics card will pull some of the load for playback.

I could go with a cheaper card, like this one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102814

It saves me a few bucks, but it is only a 3650.

What should I go with? I am willing to spend the extra money if it is worth it, but if the rest of the system is going to bottleneck the card or if the power supply can't handle the more powerful card, why waste the money?

Thanks for any help!

 

[chedderslam1]

Update:
I just looked in my closet and found my Mushkin XP-650 power supply. Could I use that? Unfortunately it looks like it has 4 20 A rails, and the newegg page for the 3850 calls for 30 A on the 12 volt. If I went with the more powerful card, would this power supply work? I would rather not switch out power supplies, but it is no big deal if it lets me use the better card and that card is the best choice.