According to The Register, Intel have confirmed plans to release a 64bit version of their low-end x86 CPU.

This may come as a blow to AMD, as their low-end x86 CPU, the Sempron, is crippled to be a 32bit-only slice of silicon. Whether or not this will make a real difference remains to be seen - the Sempron 3100+ has shown itself to be a right little screamer of a chip for being a budget part, and the addition of 64bit extensions does not seem to have had a huge impact on the performance of the P4.
Even still, perhaps AMD will take a look at their Sempron line and have a think.