Sorry, yours is like mine and I guess Nimii's all in ones - does not have the grey scale option, your best bet is to convert in an image program, or set printer to use draft setting to consume less ink, but that will still give you color.
From buy.com reviews from this printer:
QUOTE
There is no capability to print in just grey scale without converting the picture first
Your printer manual has conveniently left this info out, as did mine.
You can always use print preview to check how it's gonna look too for the net.
If you want the default setting of the printer to be to print the fast draft - meaning the fastest, less ink intensive, print setting, then go to control panel, find the printers, right click on your printer name, select printer preferences, you should see options on one of those tabs, and a box or button that says default setting, so when you print from the web it will give you a decent copy rather than a photo quality printout, that's pretty much all you can do with printing stuff from the web if it's not b&w already, or screen shot and save as image and then do like Subir says, sorry, I guess HP is not alone in doing this to their customers.