I recently moved a subversion repository to another location and had to update all the Eclipse projects to the new URL. The clumsy way would be to checkout the whole project again from the new repository URL but there is also a command line way to easily switch everything (Subclipse doesn’t offer that possibility directly though):
svn switch --relocate <oldUrl> <newUrl>
Mind that “oldUrl” and “newURl” have to be full addresses, not some kind of subdirs or relative to another.
Juist to mention it: Subversion 1.4 and 1.5 repositories are not backwards compatible and whenever you use a 1.5 client to check something in there is hardly any way to move back to 1.4 (and 1.4 clients won’t work with the repository anymore).