Sorry kids started happening around here and I forgot about your question!!
But yes you can save them as .tiff's OR you can save a copy of them in the .psp file format and that will preserve their quality also while you are playing with them!!
As you probably know, do not mess around to much fixing and changing your .jpg files.
Here is a link to a well writing article for resizing and how it should be done..
http://www.photo.net/learn/resize/
You say they come from your memory stick at 72ppi/resolution.
Under file in PSP9 click on your General preferences and then the Units tab:
Read the Default Resolution on the right side and change that number to 200 or so.
Just possibly your camera is not bringing your photos value into the PSP9 program???
Depending on how old your camera is....? I know that my older camera did not have this ability!!!
hope this helps a little.
Tracey