Ya, only single core. I'd suggest the upgrade.
I had a Athlon 2800+ up to a few months ago. Had the Clawhammer.
2 gig of DDR RAM, 66/6800 AGP video card and a SATA drive, your running Windows XP no problem for the next 2-3 years.
Of course, if you can hold out until you have the money for a dual core system that would be more beneficial.