you can use Pidgin Internet Messenger which supports both of them (if im not wrong) Perhaps you need to enable extras-testing and extras-devel categories.

first you need to enable extras devel catalog, http://nokia-n900.com/forum/nokia-n900-maemo-apps/get-access-to-more-maemo-application-catalogs-108/ may help you.

after you add, go to the application manager and search for pidgin. it should find only one result. install it. then just open the application and set up the accounts. it  supports a lot of services .

also, when installing other applications from extras devel make sure you really want to install. extras devel applications can be unfinished / bugged or not optified. but pidgin is good
when you select an application to install you can see which catalog the app is placed.

Nope  i'm here to help.
Also, sorry for the post errors, i was almost sleeping and i wrote that from N900. Anyway, they are corrected now.

Have you tried working with Conversations? The default IM on the N900 does manage GTalk, and probably even Y!