sizing .jpg for printing photos

My apologies if this is off topic. My local one hour photo developer
tells me that they can print photos from a floppy containing files in the
.jpg
format. I would want to have the output of this in 4 X 6 inch prints.

I have a dated version of MGI VideoWave 1.02 with miroVIDEO DRX
on my computer that I use for pulling images from my camcorder, or TV for
use with
my dated Pentium II occupied by Windows 95 along with PSP 7.03

Can anyone give me a few hints that will help me for cropping, sizing,
compressing,
etc. the files so that I might end up with 4 X 6 in prints in portrait mode,
and what
ever they call it where a subject might be standing with his/her feet on the
4 inch side of the print?

The images taken from the camcorder 8mm tape are either 320X240 and
can be 640X480, but the former is my preference as the latter takes lots of
file space. What pixel size should I try to end up with to have a good 4X6
inch
print?

Then, when I convert from .bmp to .jpg, should I use the high end
compression
allowed by PSP  to get a better quality print?

Thank You,

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