Extending primary partation

I have installed vista ultimate 64x in 'C' drive, which is the primary
partation of 30GB. My 'C' drive is almost full now, so i thought of extending
it. I came to know that a OS dirve cannot be extendable. Hence i thought of
reinstalling the OS. I booted with the VISTA DVD and format then delete the C
(30GB ), D (20GB) , E(20GB) drives. Now i found 2 different unallocated
space. 1 with 30GB and other with 40GB. How can i combine them. Thanks in
advance

Anto