Yes the Sapphire radeon 9550 will go in your pc, as the spec I found for the 8809 say it has an agp slot.
Before you install the new card, turn off the pc.
The graphics you have at the moment are onboard (ie dismal for gaming), when you install the new card you will have to go into the bios to disable the onboard graphics (someone else with the same pc will be able to help better as to exactly where in the bios the onboard graphics is located, as most bios differ), then put the new card in the agp slot, remove the monitor cable from the onboard graphics and on to the new card. Start your system up and the new card should be detected, follow the instructions on how to install the drivers that came with the card, restart, and you're done.
Battlefield 2 DVD Rom only - requires a DVD Rom drive to run
P4 1.7GHz Processor
128MB 3D Graphics Card
P4 2.4GHz Processor
256MB 3D Graphics Card
T1/LAN Internet Connection
According to the above it should run on your new card, but maybe not with all features on high.
Hope this helps.