Hi,
I would scan the negs and at as high a res as possible , it may take longer but will be worth it if you ever want large high quality prints off them.
After storing them digitally you can then easily reduce them in size on whatever photo editing software you have (assuming you have such software ?)
Lab quality prints are printed at 300 dpi but I have scanned 35 mm negs at 1000 dpi to give maximum potential for future use (even scanned large format negs at 2000+ dpi!)
The resolution of monitors and hence the net is 72 dpi so this is what your aiming for to put then on the web.
Hope I havnt blinded you with figures