aptitude: No solution found within the allotted time. Try harder? [Y/n]

[agou <agou@talktalk.net>]

Being fairly new to both debian and kde, I am trying to follow the 
instructions on:

http://pkg-kde.alioth.debian.org/experimental.html

in order to install kde4.

I am not new to Linux, only to debian; I used gentoo before, then ubuntu 
which I found intolerable because of the tendency to unnecessarily dumb 
down everything and hide information from the user; and because the 
support for kde seemed rather inconsistent. My debian installation is 
the latest stable.

I have got as far as:

aptitude -t experimental install kde4

which runs for a while, and then comes out with a seemingly endless 
number of:

No solution found within the allotted time.  Try harder? [Y/n]

- but no word about what is the problem. Shall I just keep pressing 
return and comtinue? I abandoned it after about 20 or 30 repetitions.

So what should I do, if I actually want to run kde4? Abandon debian? 
That would be a shame, it seems to one of the few worthwhile 
distributions around.