Hi HHawk.
To say that you want to share a partition is a little confusing - makes it sound like you're working with a dual boot scenario.
Instead, I think you're really trying to share folders between the two PCs.
With the work PC, do you connect to a windows domain? If so, security policies might be getting in your way.
Both Vista and 7 are more secure than Windows XP, and this necessitates becoming familiar with the new mechanisms. It's pretty widely felt in the industry that this increased security is making life better for users.
It's also important to know that certain versions of Windows don't permit all sharing functions. For example, Home Premium won't permit joining a domain at all. I don't know all the details of file and folder sharing with Home Premium.
You might want to try a file synchronization solution like Live Mesh. Check it out at
http://www.mesh.com. Basically, you create folders "in the cloud" and you sync these folders to your PCs. If you put something in the folder on one PC, it magically appears in the same folder on the other PC.
Cheers!
Greg [MSFT]