loopy, are you overclocking on a budget? 😀
No, I don't think it's a good idea to use that HSF on a Barton 2600+.
According to the AMD technical documents, the maximum thermal power of a Duron 800MHz and Barton 2600+ is 27.4W and 68.3W respectively.
The stock HSF's that comes with AMD or Intel processors don't usually have much headroom in them, so I don't think it's a good idea to put on the Duron HSF on a Barton 2600+.