Walmart-online printing

Hi, Has anyone uploaded the digital picture and sent them to walmart photo center for printing? I recently received the pictures from Walmart(pick-up not shiping fee!). THe resolution is great(both 5x7 and 8x10, took by 3.3MP digital camera). However, all the pictures look very dark. For comparison, I took the digital file CD to walmart loacl store and print it on Kodark printer(4.75$ for Kodark paper), the same pitcure looks very bright(may be too bright! this time, origial picture did not do any adjustment), but the resolution is not as good as walmart photo center's online print(I believe they use Fuji paper). Does this problem happend to you? Any advice? how to improve it. I can not find any brightness adjustment on the Walmart photo center web site. By the way, do you know what kind of printer they use, thermal dye(?) or ink jet(may be not). Thanks.