The one step you need to do is decide which list you want your bookmarklets to land in. Go to the list you want to use and hover your bookmark over the "Print" link. The link should go to a URL that's something like:

http://www.rememberthemilk.com/print/[your user name]/[list number]

Take that last number, that list number, and put it where it says LISTNUMBER in the bookmarklet at this link:

http://pastebin.com/H51GD1JV

In Firefox, you can even assign this bookmarklet to a keystroke. Rather than reproduce all those directions here, I'll point you to this tutorial I wrote:

http://www.reddit.com/r/bookmarklets/comments/ogzr8/for_firefox_users_how_to_assign_bookmarklets_to/

For example, I have Ctrl-Shift-U assigned in Firefox to bookmark the current webpage in RTM, and Ctrl-Shift-T assigned to this task entry bookmarklet.