Will partitioning a drive erase it?

[Keytachi]

The title says it all, but i'll develop a little bit.
I have a macbook with 80GB internal HD and one 250GB LaCie external HD as a Time Machine. Now, i only use 120GB of that for backups, so i thought i'd do a partition to get some extra space.
However i don't know if making that partition will erase the contents of my Time Machine.

Any one who could shed me some light?

 

[apfhex]

Normally, using Disk Utility, partitioning will format (erase) the drive. I think there is at least one 3rd party utility that can do it non-destructively. Boot Camp Assistant also does it (formats the partition for Windows and I'm not sure if it would work for reformat that as HFS+).