Which is better Intel P4 3.8 Ghz CPU or going to Dual core?

I am upgrading my old system from a socket 478 to 775 (im on a budget) lol And I have a wonderful Intel P4 3.8 800 Mhz FSB cpu on my list. I play a few games on my pc. Oblivion and such. Would i be ok with that cpu or should I just fork out the money and go ahead and get a dual core cpu and which kind of speed would I realy be looking for?