Networked should be fine, but you could also probably use Target Disk Mode and a Firewire connection. I would use Network because it is easier.
After mounting the Home folder from the old Mac onto the Desktop of the new Mac, in Mail on the new Mac, click on File, and choose Import Mailboxes. Choose the type as Mac OSX and continue. You will be given a dialogue to navigate to the folder from which you wish to import, so choose the Home folder from the old Mac now seen in the sidebar to this window. Navigate down through those folders (can't use the sidebar for this) to the Mail folder and then the Mailboxes folder, but no further. Now you should have a button that says Choose -- click on this, and a new type window should open, showing every xxxx.mbox folder in the Mailboxes folder, with a box that has been checked. You may not want to try all at once but there is no risk in doing so, but uncheck the box beside Outbox.mbox, as that is already on the new Mac. Click the button to now import and wait very patiently. Mail must convert everything in the mbox file of the old structure mailbox package into files placed and indexed in a new folder named Messages that will be in every xxxx.mbox folder. You will not see this happening, but that is what should be happening. When you are done, there will be some reference to each one in the Sidebar and you can try to open each one.
If you can open each mailbox, check to see if you think all messages were successfully converted. You can confirm this, in the Finder by now opening the Mailboxes folder in the Mail folder on the new Mac, and then opening each xxxx.mbox folder, and using Get Info, compare the size of the old mbox file (should still be there, although no longer needed) with the size of the newly created Messages folder.
Once you satisfy yourself that all messages have been converted in all mailboxes, you can delete all but the Info.plist file and Messages folder from each imported mailbox.
Hopefully no one xxxx.mbox from the old computer is overly large, as conversion will be more likely to have succeeded.
This all may seem tedious, but is best done since the conversion routine is often flawed.
Ernie
