time machine clarity

hey there,

i have a mid 2010 MBP running lion. my goal is to upgrade ($20) to mountain lion because my audio interface (apollo twin duo via thunderbolt) minimum requirement is to use ML. therefore backing up lion and setting up time machine is where im seeking some help.

my external is a firewire owc mercury elite pro 2 TB and i have formatted it and backed up lion on it using superduper. no partitions.

if i want to add time machine backup to my external will my Lion backup get erased. do i need to erase my HD and partition it and do a Lion backup and use time machine on the other partition. so there is where im at. do i need to jus keep my external as is and get a separate external for time machine?

im an audio engineer so my external is for logic and protools sessions

thanx n advance!

thankx Weaselboy and Fishrrman on those solutions.

i will resize the partitions and start a tm backup on it.

now getting this mountain lion which is making my head hurt. shall i buy it from...

http://store.apple.com/us/product/D6377Z/A/os-x-mountain-lion

or is there a download link that i haven't found yet?

also Fishrrman i've cloned the existing HD with SD, so next i should do step 2 once i have ML, then do step 3, then do step 4, then do step 5.

questions:

im not understanding step 3. also on step 5 is that tedious to do migrating everything over? lastly what do you mean by erasing the old copy of the OS (youre talking about the old copy on the computer or backed up on the external?)

once i've successfully been running ML i will then on a new external do a SD backup of the new ML

also on the TM partition, can i drag and drop things from my computer and place on that part of the partition without messing up the TM backup in any way? or if i wanted to drop and drag from my computer to the SD backup of my OS partition without messing up the SD backup partition if you get what i mean.

thanx n advance