dual boot in linux

i hav a 20gb harddisk.14gb i gav for win2000 server, remainin 6gb free space i gav for linux version 9.
*win2000 is booting properly
*In linux i cannot create a 3rd partition,i can create only two partitions out of tat 6GB,and now iam work on the linux without a swap partition.
*if i try to create the 3rd partiton, its displayin an error message “no enough space for allocation”
*i gav 150mb for /boot and 3gb for root

what is the problem? and how to get rid of tat?