If all you want is files, consider www.foldershare.com. I've been using their free version for years and years, and totally love it. You can have two directories that you are sharing (but before you say only two?, it includes all the subdirectories under those) in the free version.

You put the files you want to share in the shared directories, and every time one of the machines are online, it pushes the most recent version of those files to all the other machines.

I've got my bookmarks, documents, and a ton of other files that keep in synch between all the machines, just looked, 2,500 files, about 200 megs worth. Granted, I may use only a dozen of those on a regular basis, but within seconds of saving it, it's copied to all the other machines. I completly love it, and can't picture working without it now.

Microsoft bought them a few years ago, but the product didn't change at all.

If you want full remote access, then logmein works great, they have a free version. I don't remember exactly why, but I always prefered gotomypc.com, though they don't have a free version. It had something to do with requiring administrative rights on the machines at work, and that didn't work for people I didn't want to have that access, but that was a limitation of the system we had in the office, not the software.

Both logmein and gotomypc do not require a static IP address, just that you be online.