Raising only the Front Side Bus freq is possible with the K7 and offspring. But beyond 110 Mhz is quite difficult. If the mainboard you have lets you adjust the Multiplier in Bios or via jumpers, you're home free. If not, a GFD is a good idea. However, I don't know what GFD to recommend for Slot A T-Birds.
your best bet on OC the athlon, get a GFD. there is no really other way to OC it. You can do FSB, but that alone won't boost much. look into www.overclockers.com, they have a very complete database of reviews and article. you should be able to find something there. good luck.