Transferring data from old HDD to new on a laptop

Hi,
My current laptop HDD is a toshiba and is becoming slow as it's only got under 10gb out of 250 left on it. I've just purchased a WD 500Gb my passport portable external HDD. I'm thinking of taking out the WD5000BEVT drive that's inside it then placing my old laptop HDD into the nice enclosure. I read somewhere that the 500gb my passports have this drive and in tomshardware, the WD5000BEVT 500gb scorpio blue is praised highly in 2.5" HDDs.

I'm trying to figure out the best way to move my files, programs and OS to the new HDD on my laptop. As there are files I would like in my primary drive (soon the be the new WD drive) like programs, OS and documents. But there would be files that I would like inside the external (i.e. keep in the toshiba, soon to be external).

I could copy the entire contents (about 250gb) to the WD externally before I take it out, then swap the HDDs then delete the stuff from each drive, but I guess that this would be inefficient? As there is over 100gb of stuff I'd like to keep as external (i.e. just take out certain files OS, and programs from current HDD to new).

What would be the best way in everybody's experience? Software? etc.
Many Thanks.

Instead of deleting a bunch of stuff on the 250 after the swap, maybe you should just re-Partition that drive to be an empty non-bootable data drive, then copy to it all the stuff from the 500 GB unit (contains everything as a clone of the original). After copies are verified good you can delete from the 500 GB unit what you moved.

I rarely use a MOVE operation between drives for vital data. I'm much more comfortable with a COPY operation I can be sure worked, followed by my own DELETE operation later.