intel D865GBF nvidia support

Can anybody help me with choosing the highest possible upgrade for my D865gbf intel mobo.....it uses ddr1 ram...and supports only AGP graphic cards....(i do not know a lot abt these......if any info needed plz ask..and i will let know)

I am planning to cash in on a nvidia....actually the highest possible upgrade on my mobo...

what r my options without changing the mobo components????