Unless you find something in the svn book, there's only one "safe" way to do that. You push the old project out of the way and check out a fresh copy from the new server, then merge any updates. If your sysadmin is co-operative, he/she might be able to save you work by letting you check into your old project server and then move the archive to the new server where you can check it out without having to merge.
Both CVS and Subversion maintain server info at all levels of a checked-out project. In CVS it's safe to modify that info by brute force, but I'm not sure about Subversion.
At any rate, I think you've discovered why I'm a firm believer in accessing services via a meaningful hostname (e.g. svn.apache.org) instead of an IP address. If the IP address changes, but you've checked out using a hostname, you don't get this sort of trouble providing that nobody changes the hostname and DNS gets updated.
As an aside, you can retarget source archive servers in Eclipse projects under CVS. Eclipse notices the new address and asks whether you want to update your project. Eclipse makes CVS almost civilized. Now if someone would just tweak their subversion plugin to be equally civilized...
Bjoke: A "Bully Joke". A Statement or action made with malicious intent - unless challenged. At which point it magically transforms into "I was just funnin'" or "What's the matter, can't take a joke?"