Your request is not rare.
ActiveSync-ing to two PCs will cause both your PIM sets to be synced to both PCs. I assume this as undesirable for you as it is to me.
I use Intellisync to combine and sync my personal PIM sets into my Axim but be able to keep business and personal PIMs separate. It's at
http://www.pumatech.com and offers a trial version.
Hope this helps.