I need hook which is working before signup data save on new user and blog registration on BP or WP 3.0.3. Any help would be greatly appreciated.
You need to look inside the files and follow the program flow to find out about hooks and global variables to interact with.
Multi-Site Setup is a mess hook-wise, this can be pretty hacky. Some hints to far:
Standard User Registration (Single-Site)
Site Registration (Multi-Site)