Migration Assistant won't Migrate files.. not enough disk space!

How much space does finder say you have on macintosh hd? When you backed up, did you back up using time machine? To a disk or to a Time Capsule? How much hdd space did you have before you started all this?

 

You still haven't provided a few details: How big is your HDD? How much free space was there before you started? Did you create any partitions now that weren't there before? You might have to start over and delete those partitions and create a new, larger Macintosh HD partition so you can use migration.

Without those, all I can suggest is manually dragging files out of your TM backup.
1 - turn off Time Machine

2 - mount the TM backup so that "Time Machine Backups" is showing on your desktop.

3 - navigate to the backup folder (probably called your mac.sparsebundle) and pick "show contents"

4 - you should now be able to browse inside for files by date - only do this sparingly to "get you by" until you figure out the main problem so you can do a normal migration. DO NOT write to the Time Machine backup for any reason. Changing something inside might make it not work when you finally figure out things to do a normal migration.

Don't turn Time Machine back on until you have all this sorted out. It would be a shame to have your backup get corrupted before you manage to get everything you need out of it. Did you really have 300 gig worth of stuff or did Time Machine make a backup of some junk files?

I think you skipped an important step before doing the clean install. You didn't take the time to clean out your files so everything would fit afterwards.

Here are my clean install steps:

1. Survey your Macintosh HD to find out which files are using the most space. Grand Perspective freeware is good for this.
2. Delete any unneeded ones (making sure they aren't needed by the OS!)
3. Make a NEW Time Machine backup
4. Make a second backup using crashplan, or something other than TM
5. Check the integrity of both (or more) backups
6. Once you are certain all your backups are safe, reboot
7. Hold down option and pick either the Lion recovery partition, Lion recovery USB or a MacOS install DVD
8. Launch disk utility from the file menu before allowing the install to proceed
9. wipe Macintosh HD by using the erase command and set it to HFS+ (Journaled)
10. Quit disk utility and start the install
11. Pick the new Macintosh HD when prompted
12. When prompted for migration, pick the fresh TM backup you made in step 3
13. If TM restore fails for any reason, restore from crashplan or whatever secondary backup you used.

If you can manage to get back to where you were before you started, possibly by reinstalling Lion but waiting to install 10.7.1 until later, try the steps I listed above. Hopefully you will have a LOT less than 294 GB to put back this time.