My wife has a Droid X. You'll find the Intercept much less capable and the smaller screen painfully small, especially for web browsing. But it will be a nice toy.
If it's not new, you're going to have to upgrade it to froyo. You may get lucky and once you've activated it, the upgrade will get pushed to you. If not, it's not hard to upgrade it manually. There are several threads in this forum that will walk you through it.
Another big difference between the phones is the Droid X's interface to use your phone as a drive to your computer and the Intercept's problematic capability of being a remote drive with no software to make things easier. Many Intercept users have had problems with this. Again, lots of post on this issue in this forum and the Sprint Intercept forum. The bottom line is that after you've checked the obvious things, it's the cable that causes problems.
Good luck!