Hi,
I understand your dilemma. Been there, got the T shirt, as they say. ^_^
Legacy 6 will run fine on Win7. Or you can upgrade to Legacy 8, it's up to you. Legacy in 7 & then 7.5 greatly improved from 6 (in my eyes anyways) and 8 has been even more improved. I've used all versions since 3.
I had Win98 & went to XP while on Legacy version 5 then upgraded to 6. Then I went to Vista and then upgraded to 7 & then to 7.5 when it came out and finally to 8 while still on my Vista (but also have both Legacy 7.5 & 8 on a Win8 laptop) and it has run just fine no matter where, what OS or what machine. 3 different laptops and 2 different desktops. No glitches for me. I have a Win7 desktop also but, hubby uses that so I haven't installed Legacy onto it. But, I know that many others have done so, all 3 versions of 6, 7 & 8.
To switch machines, just install Legacy on the Win7 machine and on your XP machine, do a backup of your database and a backup of your media (if you have it) to a flash drive or a cd/dvd or something of the like. Then open Legacy on your Win7 machine and choose File/restore and point it to the flashdrive/cd/dvd and it will restore the database to the Win7 machine and you should be all set.
Or, you can just copy the full database off the XP machine to the flashdrive or whatever and then copy it to your your Win7 machine (into the same folder that Legacy 6 needs it) and then just open it like normal.
If you decide to upgrade to Legacy 8, then it's basically the same thing. Legacy will convert your database to the newer version and should not harm it. I've never had a problem of it messing up my database on a conversion. You just install the new version and then click to "open" your file (! a copy of the file that is, just to be safe!) and it will convert it to the new format. !Once it does that, you cannot revert it! That is why you use a copy just for safety sake.
Here is a great place to get help and great advice.
Legacy Virtual User's Group. They have lots of advice, tips and also videos. Even just to read through what they post or archived discussions, helps a lot.
https://plus.google.com/communities/102471840504878929586Hope this helps,
Val