In order to mount as "guest", you need to use another command: mount_smbfs

mount_smbfs -N //guest@server/share /some/existing/path

The "-N" is "don't ask for password" (type man mount_smbfs for more info).

As for the second part of how to create it on the fly (the path), I believe that it's not possible. The mount command doesn't create it on the fly and even the man pages mention the "correct" way is to mkdir first then mount.

See the man page for mount_smbfs.

 Considerations

For the partition, in its entirety, at the server you grant read and write privileges to everyone:

• may be comparable to guest access, which does not require authentication.

Consider the following possibilities:

• some communication, or attempted communication, by Windows 7 may be anonymous, without authentication (whether/how such communications would be logged by the server in a non-Server build of the OS, I don't know)
• writes, or attempted writes, by Windows 7 are inappropriate for something at/around the root of the partition.

Suggestions

Increase the verbosity of logging for SMB

This may be easier to achieve with a Server build of the OS.

Diagnosis at the server when the client perceives a problem

Enable the stackshot daemon then use the key chord for sysdiagnose

Preparation: enable the daemon

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.stackshot.plist

When the problem occurs: use the key chord for sysdiagnose.

For at least ten seconds after the chord, touch nothing.

After Finder brings to front the result of sysdiagnose: decompress the archive, consider the files that comprise the diagnosis.

References

stackshot(1) OS X Manual Page

sysdiagnose(1) OS X Manual Page