Please allow me to add a bit to Animal's good information. First, I think everything will be much clearer if you understand the difference between WebMail
and Typical Email/using an Email Client
. I found a nice article that defines the two--I suggest you read it carefully before reading any additional comments: http://www.basiccomputerinformation.ca/web...-email-clients/
Once you have read that you might realize that what you are wanting to do is share your photos with webmail. HP's program (which I also have installed, altho it is version 3.0 and I don't use it to share photos) will not allow you to do that. You have to use an email client. Under the Programs tab in Internet Options, you set which email client is the one you want to use to do that with--the default. You can't set it to use webmail (GMail, Yahoo, etc.) because that isn't an email client. You should have either Outlook or Outlook Express installed already, but I don't know if you have it set up yet or not. You might be able to configure your client to download from gmail, but this still won't accomplish what you want and in my opinion it is more trouble than it's worth.
It's also been my experience, and it's my considered opinion, that HP's software leaves much to be desired. They should stick with hardware. Just remember that just because you use their printer doesn't mean that you have to use their crappy software. There is other, better photo editing and sharing software out there. Since you are wanting to use GMail, I would suggest you switch to Picassa: http://picasa.google.com/
It is owned by Google, as is GMail--so there is a button in Picassa that allows you to send your Photos by GMail--or your email client if you prefer. I find Picassa much more user friendly as a whole, including their photo editing tools, which are pretty good.
All that being said, I want to suggest--make that I want to urge you, to not use email to share photos at all. Why? Because there are still people out there that have little choice but to use dialup internet service. If they also use an email client, then they have to download those large photo files and it ties up their client where they can't check their other email. It can also quickly max out their email storage space limits. Instead, consider using a photo sharing service, where you upload your photos to an album on a server and send links by email instead of the actual photo. The recipients can download any photos at their own convenience. HP's software provides such a service thru a third party (Snapfish), but again, they don't make it easy to use, at least initially. Here again, Picassa's Web Album is much easier to use. And it's all free unless you need more than 1 GB of storage for your photos.
Now it occurs to me that you may have tried to use HP's photo sharing/Snapfish service. If so, for the button to work, (you still have to use email to send a link to the web page where your photos are stored) it still has to know which email client to use. So if you still want to use HP, you need to find out which client you have installed, get it set up like you want it, then go back to Internet Options and under the programs tab select that client as your default.