I'm not sure you can access the shared drives/folders on a Win7 machine from outside, without first providing the connection credentials (i.e. the same Windows logon and password you use when you boot the Win7 machine and get to the Welcome screen).
And I don't think that can work without a password. Can't have username but no password, and certainly can't have no username and no password. Though this might work for booting up your Win7 system and bypassing the Welcome screen or avoiding entry of a password, it won't work for permitting remote access from an external machine.
In other words, I'm not sure you can provide shared access to your Win7 system without requiring a Windows logon (at the Welcome screen) with both username and password. This is designed for your protection and security, and really allowing entry to your Windows system without requiring a password is just an invitation for havoc from hackers, as low a likelihood as you think that is for your own situation.
I've had to deal with this with friends, who also have multiple machines in the house (e.g. husband and wife) and they never had bothered to have a password for either machine. They just wanted to power them on, and bingo Windows desktop appears. But when trying to connect the two via the LAN (i.e. through their home router) it was not possible to see the contents of either machine from the other, because there was no username+password to provide to the credentials dialog. I had to convince them both that all it took was Control Panel -> Users -> set password, on both machines (which would need to be entered only once per every-so-often when the machine was actually re-booted and the Welcome screen logon appeared), and that would be the end of the problem.
They agreed, and are now happily sharing data back and forth between the machines. Win7 is more secure than WinXP, and this is just one reason: Windows logon password required if you want to make your machine's allowed shared resources available to outside users. And of course, you can check the "remember my credentials" box, so this dialog will appear only once on the XP machine, the very first time you connect to the Win7 machine. From that point on you'll never again be bothered.
All it takes is adding a password to your Win7 user logon, and then entered on the Welcome screen Windows logon (whenever and if ever that you do boot the Win7 machine), and then just once that very first time you connect to the Win7 machine from the WinXP machine. Seems like a tiny price to pay for the added security.