I had two partitions on my HD under windows. I decided to install Ubuntu, hoping it will install on partition where was Windows, so I transferred all my files to second partition, and now I cannot access them.
But is that partition still available? Did you install on the whole HD or you explicitly specified the partition to install onto?
I'm thinking of two things now: 1) You installed ubuntu on your harddrive, meaning, it combined those two partitions together as one, and installed on it. All your files are gone, thus :( 2) Your partition is still available, but you'll have to mount it. Try mounting it by clicking on its name in your Home Folder.