Merge and remove user accounts?

Thank you in advance for any advice, I'll try and keep this clear on what I would like to achieve....but first a bit of background...

Splitting up with girlfriend and we share a MacBook, 320gb HDD, upgraded from original 120gb HDD (currently in an USB enclosure used as an external drive) running Snow Leopard, which I have agreed she can have as I'm going to purchase a new MBPro in near future.

We have separate user accounts, but I have data (Photos, Documents etc.) in her account but not in mine, which I want to keep.

I use Time Machine to backup to an external firewire HDD 250gb, which is at capacity (245gb); and I have an Airport Extreme, with a 1.5tb HDD connected which I use as a media drive.

So here is where I want to end up, which I think is the easiest way to understand a route of how I might get there....

I want to give her the MB with the original 120mb HDD reinstalled and only her user account installed with administrator privileges, no trace of my user account. I want to store all my data on the 1.5tb HDD until I buy MBPro, next month, and be able to put my user account on it, having merged the two user accounts.

Hope this is clear and someone can help me work out a method of doing it.

Thanks in advance.

There is not really a way to merge the 2 accounts.

Couple of ways to get it done:

Create a TM, CCC or SD! backup for your account on the external.
Copy the particular files from the 2nd account onto the external
When you get the new Mac use the Migration Assistant that opens on startup to import your user account and then move the 2nd account files onto the Mac.

or

Log into her account - place a copy of the files you want into the Public folder.
Log into your account - move the files from that Public folder into your account.
Then create the backup for your account.

Personally, I suggest using either SuperDuper! or CarbonCopyCloner for the backup.
This allows you to boot to the backup and verify everything is there and working.
Not so easy to verify a TM backup.
But note: nothing but the backup will be allowed on the partition with SD! or CCC.
You'll need separate partitions for the backup and additional data with those 2 options.

Thanks for the reply bobtomay.

So if I partition the external 1.5tb HDD to create enough space for all the data on the MB and then CCC the internal 320gb HDD to the external drive, can I remove the 320gb, install the original internal 120gb HDD and migrate back just her user account? I will then have a copy of both user accounts to migrate back to the new MBPro, after which I can switch around the data, and delete whatever I don't want.

I really don't know if Migration Assistant can be used to import only a single user account or not. Maybe someone that knows will pop in.

In case you can't -
You could create a backup of the 320GB drive to the 1.5.
Then delete your user account from it.
Then grab CCC and have it create a bootable clone from the 320 to the 120 and then change out the drives. Just boot to the 120 before you start changing the drives out to verify it's bootable and working.