As far as #1 goes, 2011 is just about as far away from 2007 as you can get and still be in the same package. To be fair, most of the UI changes were in 2008, but there will be a lot of getting-used-to.
Ferris - I also have gone from ver7 to ver11. But I bought a new machine (64 bit Win7) for Sworks only. I still have ver7 on a XP op sys machine.As soon as I am completely secure with my level of comfort with ver11, Solid works 7 will be gone. 11 seems to be easier to work, so far. Art L
It iterate the comments of others, there are substantial differences. Most of the changes occured in 2008 version. It's some of the bigger interface items you might notice.
1. The command manager is now a tabulated ribbon.
2. The "S" key now brings up quick access menu at your mouse cursor location.
3. Scoll bars are turned off (you can turn them back on).
4. Design tables are now accessable on the configuration tab of the propertymanager.
There are likely literally 100 major differences, so check out the What's New at Ricky's website (as mentioned by another commenter).
As far as trying to run SolidWorks 2007 on a 64-bit Win7 system. You should be able to in capability mode (a Win7 option). But know that you will still be limited to just 2GB of memory. If you have large assemblies, my recommendation is to upgrade.