Whoo, yeah, a lot of misinformation here.
You do not HAVE to OC your RAM when OC'ing the processor. Like DJ said, if you have access to raise the multi, that won't effect RAM speeds, and 2, you can lower the FSB:RAM ratio in order to avoid OC'd RAM speeds.
With that said, you do not have access to raise the multi with your chip, so thats out.
Now, one thing I don't know is what RAM speed you have and what the FSB is on the old XP chip, but you might have overhead with your RAM so you could OC at 1:1 without OC'ing your RAM as well.
For example, if your FSB is 133 (533 total bus) and you have PC3200 RAM (200Mhz speed), you have a lot of overhead to OC with.
Now, I am not familiar with the Athlon XP chips, but keep reading and you'll figure it out. Also, like DJ said, you can still usually get a little OC out of valueram, you just have to play with it and see what works.