Windows Media Center - External Drive

It will be OK.

There won't be any issues! You can go with your External Disk Plan!
All the beest!

The only thing to watch out for is accidental disconnection of the drive. If you go into device manager (Start -> right-click Computer -> Manage), navigate to the drive in question, double-click the drive and select the "Policies" tab, there's a "Quick Removal" option. If you choose this option (which is the default for USB drives) the drive turns off caching which means your it's is less likely to be corrupted if it's accidentally removed - but it will hurt performance a bit. Choosing "Better performance" will enable caching but at the risk of data corruption if the drive is accidentally removed.

If you're just using the drive to record and view movies, you probably won't notice the performance difference. But if you copy a lot of files to the drive the copies will probably take longer if write caching is turned off.