The answer to your question is: yes and no. Yes, if you resize a partition, you will loose data; no, if you make a backup first which you can restore after resizing, you will not loose data.
Get Knoppix (download and burn to cd, or buy the cd). While you're at it, use
www.google.com/linux and look up Knoppix cheatsheets, which give you commands to use when booting Knoppix (it's German; if you want to see English or some other language, you'll need the appropriate boot codes).
Make a backup of the partitions you propose to change in size (boot increasing and decreasing). Changing the size will not move the files, only change the geometry of the partition. Ergo, the backups.
Boot Knoppix, and use cfdisk to resize the partitions (which will also rewrite the partition tables, if Linux partitions are involved). Remember that the root (/) of the filesystem must be flagged as bootable. Then, while in Knoppix, restore the backups to their respective partitions.
That ought to do it.