if you set up an imap mail account on your phone it WILL delete the messenges in the inbox on the remote machine, just like an IMAP account should. if you want to just get rid of all the wasted space on your phone but still preserve the messages in your inbox on the remote machine you can just move all of the messages on the remote machine to a temp folder, delete them on your phone, then move the messages back to the inbox. the next time you do "send and receive" on your phone the messages will be loaded again, so i guess just don't download your messages if you are low on space.
if you wanna back up your sms's, mails, etc download the trial version of message storer: http://www.symbianware.com/download/messagestorer_uiq/messagestorer_uiq.sis
i had to uninstall the pc suite for p900, install the pc suite for p800. go into the phone languages folder, click on the very last norwegian language file called "Norsk_cxc162001 R2A.sis" then go into the phone then control panel then language then choose norwegian and then it was installed!
here's a 30 day trial for a file manager on your pc that gives you access to ALL your files. found out that you can't copy a whole folder, you can only copy over groups of files, ie. you select a bunch of files (not folders) and can drag them all over at once, but not a single folder. don't know maybe it's because it's a trial.