I've installed ntCVS, WinCVS, TortoiseCVS, SVN and TortoiseSVN in parallel on several machines using WindowsXP and didn't have any problems. We are in the same situation as Michael described, in the company we're using CVS (doesn't matter which client WinCVS or TortoiseCVS) and with CodeBlocks i started with SVN and TortoiseSVN. often i use the TortoiseSVN to get information of modified files, for updating i'm using the svn-client callled from batch-files (as i did with ntcvs-client) because i manage the update-logfiles automatically.
First i was suspicious if all programs for CVS and SVN are working in parallel without unwanted interaction, but after using it now a few weeks, i can say it just works !