Will 7800gt work?

Hello this is Andrew, owner of a Dell 8400. I currently have a 6800gto in there now and was wondering if the 7800gt will work with full potental? My main concern is the power supply, will the one in there now be enough or do i need to upgrade? Any one with a 8400 if you have a 7800gt plz tell me how it is working for you and stuff like that.

 

 

system specs

 

Dell Dimension 8400
Intel P4 "Prescott" 3.4GHz, 800MHz FSB
2 GB DDR2-533 RAM (4x 512MB Dell)
150GB Maxtor SATA HDD i think
16x DVD-ROM drive

Dell 6800gto
Creative Labs Sound Blaster Live! 24-bit
19" flat screen lcd