Hah, OK. Explanation:
Obligatory speed chart:
133MHz = 266MHz DDR = PC2100 RAM
166MHz = 333MHz DDR = PC2700 RAM
200MHz = 400MHz DDR = PC3200 RAM
The northbidge chip (the chipset chip with a heatsink on it, near the CPU) runs hotter as you run the front-side bus faster.
So it needs more heat dissipation as it runs faster. AFAIK, the L7S7A2 does not allow multiplier adjustments. A 2500+, at 1.83GHz, is running at 11x the front-side bus speed. In this case, 166 2/3MHz * 11 = 1833MHz. Increasing the FSB speed increases the CPU speed. 200MHz * 11 = 2.2GHz (3200+ speed).
Typically the heatsink, which isn't great to begin with on that board, is attached with double-sided tape...not the greatest. So it gets too hot when you run it faster (like with the FSB at 200Mhz). Aftermarket northbidge heatsinks are then required. The Zalman ones are awesome

. One of them on it would allow you to overclock to the limit of the chip itself.
If you had mentioned overclocking earlier, I would have steered you to the Abit NF7. However, the 2500+ should be fine for a year or so. I'm still running an 1800+, as newer games seem to be using more video card and are stressing the CPU less (not that an Athlon64 doesn't have its place, but is hardly a requirement if you're on a real budget).
With no overclocking, the SiS746 chipset is as fast as single-channel NForce2, so right up there for a nice budget machine, and the chipsets have made great differences in performance (I can really feel the difference from a KT333 to NForce2 single-channel).