Miscellaneous laptop discussions : HELP Processor CPU Speed decreased?

HELP Processor CPU Speed decreased?

Hello everyone, i own an inspiron 9300 with a 2.0 GHZ Centrino, 1gb ram 100gb hd. I recently noticed a decrease in my CPU speed, which i know is 2.0 GHZ, when i tried the CNET vista readiness advisor, it said i had only 733 mhz!! i thought it was a software mistake, but then i right clicked on My PC and found out that yes, it says, pentium M processor 2.0 Ghz, then right below it says 798 Mhz 1gb Ram. i found it weird but then i thought maybe i hadnt seen it before.. then i formatted my lap new partitions and stuff and then i saw processor speed was up again at 2.0 Ghz.both besides the cpu name and the Ram..
then a few hours ago i noticed my system to be a tad slower than usual and by curiosity i right clicked on my pc and the mhz are back to 798!!! what;s with that? i know my processor has Speedstep, but the laptop is plugged to the AC so i see no reason to do that. Does anyone know what's going on? is it a software i recently installed ?(messenger, autocad, photoshop and similars basically)