I have no experience with the T60/ATI x1400, but I run or have run Ubuntu 10.10, 11.04 and 11.10 on T61, R60e and X60 and never experienced problems like you describe.
I installed the mint 11 LXDE on a R31 a few weeks ago and had no such problems with the install. I removed it because I (unlike everybody else it seems) like the original ubuntu/lubuntu/xubuntu distros a lot better than mint.
You should be able to install tpfanco from here: http://code.google.com/p/tpfanco/
and be able to control you fan/find your own settings.
If I remember right you should also have a program called "Systemmonitor" in the mint distro, open it and find out what process it is that taxes your cpu.