Select "Ubuntu" from this link to the MySQL workbench page
You will have a choice of:
Ubuntu Linux ver. 10.10 (x86, 64-bit), DEB
Ubuntu Linux ver. 10.10 (x86, 32-bit), DEB
and 2 slightly older versions:
Ubuntu Linux ver. 10.04 (x86, 64-bit), DEB
Ubuntu Linux ver. 10.04 (x86, 32-bit), DEB
As you can see there are only 10.04 versions but you can download the .DEB you need and when it is done downloading Ubuntu Software Center will open up with this screen:
and the rest is just normal Ubuntu.
I needed it myself (mysql-workbench-gpl-5.2.33b-1ubu1010-i386.deb) so I can confirm it works.