It shouldn't be a problem. I have converted 5.5 files to 8.0 & 9.0 with no problem. 10 shouldn't be different.
Thanks so much for your knowledge.
I *highly* recommend FMMigrator from .com solutions. After converting my 19 file fm6 solution to filemaker 10, I used FMMigrator to consolidate the files into one file with separate tables.
The whole project took me about 10-15 hours, where as doing it manually would have taken perhaps 200 or more. (assuming I have the knowledge of all the gotchas, which I don't).
Even though FM 10 upgraded the FM6 files very effortlessly, the solution was still broken. Consolidating to a single file has been very helpful in debugging and rewriting scripts.
No one guarantees no hitches...but it should be fairly painless. Maybe even hitch free if you're lucky.
Take the standard precautions, back it up a couple times first and upgrade a copy. When I upped from 5.5-8 it required a whole rebuild to get onto the relational Table Format rather than the relational Dbase format.
And play test all your scripts (ALL your scripts) before you put it out for public use. I had hitches galore in my scripts (I didn't write 'em...maybe they were hitched already...).
Then look through the layouts and dust 'em off, resize and realign. If it goes well, great. If not, you'll still be live with FMP6 and you can always import the records after you get it all worked out.
Go for it...it's worth the upgrade. Good luck!