Hard Disk Monitoring

Have installed on XP box that has been updated with dual boot to later Windows system (Vista). If I uninstall HDS Pro from XP, may I use same license to install on Vista system? Both are on same drive, separate partitions of course.

Yes, of course.
You may even keep it under XP as well, because your license is connected to the current computer, not the OS.
This is the same computer and only one OS (XP or Vista) can be active at any given time, so you can use under both.

Also if (under XP) you use Configuration -> Update -> Backup configuration to save everything (statistics, logs, registration details, etc.) to a single file, you can re-load that under Vista by Configuration -> Update -> Restore configuration.
This way you'll have immediately all settings, and the statistics/logs collected previously under XP.