When I click the install link, the browser opens a page with this...
[install]
catalogues = Fring; extras
package = fring

[Fring]
name = Fring
uri = http://reg.fring.com/repository/
dist = chinook
components = release

[extras]
name = maemo Extras
uri = http://repository.maemo.org/extras/
components = free

I tried the application manager install on page 3 of this thread and it worked like a charm.

@ramkre
thanks for recommending nimbuzz. I'll send them an email and try to install it.

Edit:
hmmm. I started the app and registered a user name. It then tried to login and the status is always stuck at logging in.
I'm using a WLAN and can use skype and pidgin fine. I don't think its the same problem as the other users were having as they couldn't even get the app to run.
Is anyone else having this problem? The only other thing I can think of is maybe the ISP throttles some P2P apps and maybe they think I'm doing illegal downloads or something. Well a pretty wild guess anyway.
Oh and one other thing I noticed. The app doesn't realise if I am in on or offline mode and doesn't relay the appropriate message.
Edit2:
Ok it works now. It seems the app needs a stronger wifi signal to run than other apps.