I have an almost identical setup (MBP and Airport Express connected to an iP4300) and printing out photos in iPhoto onto Glossy Photo paper works really well - so you should be able to get good results.
Can you see your printer if you look for Bonjour Printers when you are setting up? That is where I find my wirelessly connected Canon Printer when I look for it.
As suggested above, the likely source of problems is something to do with the printer driver. My guess is it might just be the setup options.
- In your print settings check that you are choosing the right kind of paper in the Quality & Media section of the printer preferences. The way ink is used varies quite a lot between, say, glossy photo paper and ordinary paper. You may also want to try using a higher quality setting as that will use more ink to get richer colours - draft mode prints will be pretty washed out.
- Check that in Color Options you are using ColorSync rather than None or Driver Matching.
- Check through the other pages to see if some setting is oddly configured. Play around with the settings a bit if you feel like experimenting to see if anything you do fixes things.
My best guess is that something in your printer setup is amiss and playing with those setting should fix it. The thing is, your computer thinks the wirelessly connected printer is different to the directly connected one and so you may have different setup options chosen that are affecting your print output. But the driver is going to be the same one - so that's what suggests just a configuration problem.
MacBook Pro 2.0GHz, 2GB RAM, 120GB HDD Mac OS X (10.4.9)