Will Bitlocker make it impossible to read my files from my dual booting Ubuntu OS?

"Yes.

Bitlocker is whole drive (partition) encryption, it has its own bootloader from start to finish. It is the easiest solution for encryption.

You may even have a problem booting into Ubuntu all together if your machine has a TPM chip as Bitlocker ties in to that to check integrity.

Your best bet would to be have a partition used just for moving files in between the two systems.

You may also want to take a look at using Truecrypt as this can achieve what you want very easily. Alternatively, if you want a Microsoft Solution, Microsoft have a option called EFS (Encrypting File System) that works very well and can do what you want, if not a little complicated to learn / get into.

AFAIK, EFS cannot be read from any NTFS compatible driver/app in Linux, where as you should have no problem using Truecrypt in a cross platform environment, so you could even encrypt everything and still open it up in Ubuntu."

Alternatively you might also try an encrypted EXT 3 filesystem that you can access from windows using FreeOTFE. I tried Truecrypt before, but especially in combination with SVN, which causes a lot of file accesses during an update, truecrypt was very slow.