So I finally got printing all worked out on my captivate. I have a wireless printer and really want to leave the laptop on the desk and use my phone for everything. The one major problem has been printing. Finally, here's an answer...
To Print from your Captivate, it will cost you about $4.50 (or limit yourself to 3 docs a month.)
General Printing - test this first
Get PrintBot from the market (free version to test out - supposed to cover 2700 wireless printers)
Open it and setup your printer. My settings are...
Network Connection : Protocol - Auto Printer - choose your own

Printer : Re-select your printer
And print a test page. If this works, you are in business
Printing an Excel or Word Document:Printbot is great for pictures and pdfs, but it doesn't print office docs, so those that your coworker emailed you just sit there

So here's the great workaround.
First make sure you install these two programs:
From the market, find and install google documents, open it and sign in. Make sure you can use this on your cappy.
From the market, find "My Docs - Google Docs" (by RCS, LLC), install it and sign in.
Now you are about ready! Don't give up hope to soon!
You must upload your file to Google Docs, but for some odd reason it doesn't allow you to upload xls into it (unless I'm and idiot and can't find the upload button). But "My Docs" allows this. So open up My docs, click upload, and choose your file. It will be uploaded to your google docs account. You can close mydocs, it has served it's purpose.
Open your google documents (called "Docs" in the app drawer), find the file you uploaded (don't need to open it), from the arrow on the right side - open the pull down menu and click "SEND", choose "PrintBot" from the menu and your doc should start to print. Whew! Lots of steps, but it's done and printed. Caution! Watchout for multipage excel files, it will print each and every worksheet.
And Finally Printing Email from Gmail:
For some crazy reason, none of these programs interface easily. So you are in your gmail app and want to print off your free redbox rental code or some password you keep forgetting. Leave the email alone and open up your browser (yep, back to the www).
Go to the online version of mobile gmail. Sign in and open the email you want to print (I set up a shortcut on my homescreen). On the right side of the email, open the pulldown menu (double down arrows) and click "Print". This will open up google cloud print. You should have an option to "save to google docs" where it converts your email to a pdf and stores it in google docs. Then click "PRINT", it will create a pdf document of your email. you can close the www, or just surf around for a while...
Now back to google documents on you phone, find the pdf, click the menu on the right, click send and send it to Printbot. It will print your pdf.
And that's the whole 99 steps to printing documents with your captivate.

Actually it works pretty quick as long as you use your home wifi. I tested it with excel, word, and gmail files.
Good luck - Will