It depends on the core. Many 2000+'s are of the Palomino core, which don't overclock worth much if anything (you'll hit a brick wall with the Palomino core at roughly 2200+ speeds). But if you're talking about the Thoroughbred- and Thorton-core versions of the 2000+, you'll likely get a CPU which can overclock to 166+ MHz FSB speeds (effective "333+ MHz" FSB's) on stock voltage - and some of those can even overclock to 200MHz ("400MHz") FSB.
Keep in mind, it has to be thoroughbred B, I have a 2200+ Thoroughbred A and it could only overclock to a FSB of 144 roughly. The B series had a more cleaned up core design and hence the difference in overclockability.
Reading the Processor Electrical Specification chart it says the Core Voltage Upper Limit for a Athlon XP 2000+ is 2.0V, is that the highest amount of voltage that this CPU can receive?