You will need a cable to tether your phone to your PC, and turn USB storage on (the phone), at least that is how I do it on my run of the mill LG LS-670 running Android 2.2. XP or Windows 7 should recognize your phone and treat it as an external drive. If you don't want to bother with the cable, you can always email it to your PC's email address, and save the attachment.
I have found that you usually need to set your resolution to the minimum the phone will go, usually 640x480 and set the quality at normal to even have a shot at getting under the 100K limit, especially if the image is "busy". I usually use a program like Gimp to edit the picture before posting it. You can also do cropping, light and color balance corrections as well as resizing. your images before posting.