Ok, someone was able to upgrade the Presario 5000 to 2.6GHz:
http://forums.tweaktown.com/showthre...6&page=4&pp=10
Check the last four posts.
What you probably also need is a BIOS update, yours is very old.
The upgrade would cost about $155:
http://www.pricewatch.com/prc.aspx?i=3&a=12798