Sure.
Remove the battery first.
Then, remove the cover that is adjecent to where the battery sits - it has a little picture of a cylinder on the cover. It takes three phillips screws.
Once open, IIRC, you just have to remove 2 more...
it probably will. The mounting locations of hard drives is pretty standard. Dell wants to keep their supplier options open, so you can drop in hard drives pretty much at will.
I've replaced hard drives on both my 700m and my kid's...
This is more evidence that you're overheating.
The Intel processors will, if they detect that they're getting too hot, internally reduce the clock rate to reduce their power dissipation and therefore their temperature.
When there...
It sounds as if it might be a thermal issue.
I'm not familiar with the Sony notebooks, but look around for a heat sink for the processor that needs some serious blowing out with some compressed air.
http://www.pbus-167.com/chc.htm
will work on the Dell Inspiron 700m (at least it works on mine).
It will monitor both the hard drive and the CPU temps (amoung other things).