If you are scripting on IMVU, IMVU inc already has jQuery installed on their site. However, IMVU inc uses jQuery version 1.8.3 and they block users from adding their own versions by blocking external scripts. They do this by removing the src attribute from all script tags. This means that if you have a jquery script you wish to use on IMVU, it has to:
1) be compatible with 1.8.3
2) can not use external scripts <script src=""></script>
Now, there are ways around this. You could load your entire HP from an iframe, so they code is all loading on an outside site owned by you. Or, you could try using javascript to connect to external script after it has already loaded.