Sun does x86 boxes as well.

This mention of HP offering existing Sun users the switch to HP systems got me curious. How does this sort of thing happen? These users are probably using Sun UltraSparc chips, perhaps with Solaris and other software compiled for Sparc. But whatever you're running there probably won't run on HP natively if HP's systems use x86 or non-Sparc chips. Do they port users' apps and OSes to run on x86 (or some other chip)?
Or do they offer new OSes and apps that run natively on x86 that have the ability to work on their existing data (just like, say, the way OpenOffice can replace MS Office and work with all your data)?