Best AGP card for 1.8ghz processor?

i cant seem to find the create new topic on... so ill ask for help here!1. i have a 1.8ghz single core sempron processor. what is the best agp graphics card i can upgrade to without bottlenecking? i know my processor is slow but a new one is out of the question cuz its the only kind of processor my mb supports and i dont have enuf $ for a new pc. 2. also, i used to have an ati radeon 9550 card but when playing games with it every few seconds it would say the graphics accelorater was not responding or somthing... does any1 know if that is caused by a problem with the card or with my mb? and dont worry bout my power supply ill get a new one to fit my new graphic card needs.