Excel 2007 file save problems

I have a HEAVY excel user that is continually having issues with excel locking up. He is the kind of user who will have 12-15 excel files open at a time, and they will have LOTS of formulas, and lots of links to other files. All these files are located on a network share.

He WAS using a Lenovo T42 laptop with a 1.8 Pentium M cpu, a gig of RAM, Windows XP with Office 2003, and although he complained about it being slow it worked.

We bumped him up to a new Lenovo T61 laptop with a duo core 2.0, 2 gigs of ram, Windows XP, and Office 2007.

Fairly regularly, either during an autosave or a manual save, excel just locks up. Task manager shows excel at 50% CPU rock solid, but excel is doing nothing. The laptop is responsive otherwise in other porgrams, but excel is toast and needs to be manually killed, and all the work is lost.

All service packs are installed, machine is up to date. Any pointers??