the question, what files are you trying to transfer? I personally prefer a clean install. It can take a little more time, but everything will have the latest drivers and software.
Some stuff like movies, game saves, music, and so forth, can just be transferred to an external drive, so they can be transferred back. This can be most time consuming. Other stuff such as program settings, may be able to save if you know what file they're kept, and may be able to transfer or copy. Otherwise, you can just make a note. On the same topic, some settings are going to be different since it is a different OS which may have new features for a program(s).
The biggest issue may be you have programs you no longer have installation software/disc. That's just an issue with limited resolutions. You try to download it somewhere, borrow from someone you know, and so forth. But it could be a time to see what else is out there. It's also possible that a program will not run on Windows7. I had this issue with a invoicing program going from XP to 7.
On a side note, there is a registry hack for Windows 7 so you can use the Upgrade version and do a clean install. You will need to be comfortable with doing editing registry and doing some command line. It's sounds worse than it is. It's really easy overall. method two