100 degrees certainly does seem way over any operating temp I have seen for a cpu, I am surprised it is still going. What program are u using to monitor your temps/fanspeeds, I would recommend 2 programs, Fanspeed and CPUID Hardware monitor. I take it as a given that you have cleaned all intake or exhaust fans? Also undervolting a cpu in your bios can cause extreme cpu overheating have you checked the HP website for any driver bios upgrades?
I wouldnt mess with anything in your bios manually as this can be seen as "overclocking" and void your warrantee, have you contacted PCWorld to see what they have said, would be intresting to see if they said 100 degrees was an acceptable CPU temp. They should be your first port of call, I hope none of your upgrades have voided your warantee either.