Jeremy, while your suggestion has some merit, I would argue that having him abandon Windows for a Macintosh simply means that he’ll have to go through two learning curves instead of just one. Plus having to spring for new versions of applications for the Mac, plus having to buy new hardware since Apple doesn’t let MacOS run on PC hardware, plus. . . .
Traveller, I would suggest setting up Linux on a second machine (or on a second hard drive, or on a second partition – depends on how cheaply you want to get off and how much trouble Windows gives you on repartitioning). You can try to find equivalent applications, see what works and what doesn’t, and learn what the new commands are. Eventually, you’ll feel comfortable enough to switch, at least for those parts of your work that you can switch over.
If you use a second PC, you can get a KVM switchbox (keyboard-video-mouse) so that you don’t have to switch cables around when you want to use the other machine (whichever one is “other” at any given moment). I don’t know what prices are like for barebones PC boxes right now; in the U.S., you’d be looking at maybe US$400 to set up a second box.
If you use a second drive or partition, you’ll have to reboot your machine each time, but could do it for either US$60-ish or US$zero-ish.
As far as “what is Linux”, Linux is all things to all men.
It’s such a general question that it’s hard to answer. You will need to learn the usual commands (in many cases, the same as in MS-DOS, e.g, “cd” changes your current working directory), and will need to search for equivalent programs for the ones you use under Windows.
Star Office can read some Microsoft file formats for Word, Excel, and so on. I don’t know what the compatibility problems are, if any. I doubt that they would be able to handle VB scripts.
WINE, the Windows Emulator, can be used to run many Windows programs. I believe they use MS-Word as their benchmark, so you should be able to run at least the older versions of that (maybe not Office XP’s Word, though, not sure).