New low-end gaming machines?

I'm setting up 3 computers to play games on! My 2 sons and I want to be able to play on-line games together like Battlefield 2142, etc. We have 3 mismatched systems now that aren't working out real well. Therefore I want to buy 3 identical systems that will work, but won't put me in the poor house. Since Circuit City is going out of business I checked there first

I was able to pick up 3 HP Pavilion a6600f computers really cheap (under $400). I then found 3 XFX Geforce 9600GTs that I believe are overclocked. Once I install the video cards and take out my 2 year old Creative Gamer audio cards from the old computers how will these Pavilions stand up as gaming computers? Do I need to upgrade the power supplies and if yes, what's a good, economic option since I have to get 3 of them?

Thanks in advance for any and all help!

http://www.ciao.com/HP_Pavilion_a6600f_Pentium_Dual_Core_E2200_2_2_GHz__16284800 Note the PSU is 250w (at bottom of page) also:

http://www.legitreviews.com/article/666/1/