If you 9.10 is working fine and set up just as you want then probably
the last thing you want to to is upgrade it to 10.04 !! Upgrades have
always be an issue and if it does go horribly wrong there's no way to
roll back to your working 9.10 :-(

Adding a second HD for 10.04 is a good suggestion and would allow you
to have your 9.10 still available until you have 10.04 set up as you
want. It is possible to save the package list in 9.10 to a test file
and then use that to install all of them back into 10.04 - where you
may fall down is with packages that are no longer around. Also there's
the issue of 32bit vs 64bit - i.e. if your 9.10 is 32bit then putting
10.04 64bit on would be better done as an installation from scratch
and build up from there. Not as quick but probably less hassle in the
long run :-)