Resising CAN be done providing you have 2 sets of tools (Windows and Partition Manager) and your Linux install disk.
so do the following
1) Boot into Windows.
2) Run Partition Manager to Move / resize your Linux partitions --you can even move on to a different Disk.
3) Now boot your Linux Install disk --and choose 'Recover / Repair system".
The recovery will adjust the fstab entries (necessary if you've moved the partitions) and re-create the GRUB boot loader --also necesssary as the pointers will have changed.
Then you are away to go.
Incidentally if you have something like GHOST or ACRONIS true Image (V9 --Desktop version not the Server edition) you can create backup partition images of your LINUX partitions as well as Windows and it's great for recovery -- saves a load of re-installs etc etc --and with acronis you can make bootable media so you can recover even if you hose up the whole system.
I don't buy much commercial software -- but I really can recommend this package --it saves so much time and hassle -- it takes around 3 mins to restore an 8 GB Linux partition from Disk and around 10 - 15 mins from a DVD..
If you do restore partitions this way you'll still need to re-run the "repair" function to re-create GRUB.