If I erase and install Lion, will my exisiting Time Machine Back-up be overwritten?

Since upgrading to Lion, I have experienced problems with permissions and having to repair the disk.

I have decided to do an erase and install of Lion, but would like to clarify a few things about the time machine back up.

Firstly, once the operating system has been re-installed (I do not intend to restore from backup), will my current time machine back up continue to operate or will a new back up need to take its place?

Secondly, rather than restoring from the back up (as I have alot of redundant apps), am I able to select certain apps/app data to restore? (If the answer to the above is 'Yes' then i assume that this could be done by entering time machine once I am up and running).

Thanks