I would Download PC wizard http://www.cpuid.com/download/pcw2005_v164.exe
to verify that your motherboard doesn't already have a Thermometer built onto it, although builtin thermometers are not always accurate...
and screwing a Regular Thermometer to your case doesn't sound like a bad idea :-P
IBM/Lenovo T43 2687DSU
Pentium M 2.0Ghz
1024 MB (DDR2 SDRAM)
80 GB Ultra ATA, 5400 RPM
Windows XP Pro
64MB ATI MOBILITY RADEON X300
Integrated 802.11A/B/G, Bluetooth, 10/100/1000 Eth.