try not to confuse the different things going on.
Your dongle connects your laptop to the mobile phone network. Your dongle is ALSO acting as a wireless receiver for wireless networks (not mobile networks) – but as I said, there's probably one inside the laptop anyway. Your mobile broadband package probably bundles wireless access in certain locations for free as well.
Your desktop is connected to the fixed line (telephone) network via the adsl modem box.
Your laptop almost certainly could also connect to your fixed line service if you upgraded your adsl modem to a wireless one.
setting your email up depends on what you use to access it and where your mail is hosted. If you have the same client software on both PCs then the easiest method is to copy the settings on one.
I may be wrong, but if your adsl modem is also a router you could connect your laptop to it and then map a drive on the desktop to your laptop and then copy the files across you want, but Im not an IT boffin so cant be sure or explain quite how it works – only that Ive done something like it here at home.