It will work as a "raw copy" if using Win 95, 98 or Me. It won't work in Win NT, 2000 or XP (or at least you should reinstall the boot manager with other methods).
P.S. you can copy everything EXCEPT the virtual memory (win386.swp, as I remember).You'll find it in either c:\ or somewhere in \windows
I'd say to copy all the data, repartition but leave free space for Linux, then copy data back (you may even archive it on 2-3 CDs). But you'll need an Win98 emergency disk (somewhere in control Panel you can create it - Add/remove programs/Windows setup/Emergency disk)
Maybe you could re-partition (with PartitionMagic) your disk, so that you could save your main partition on the secondary partition?
for the start, you might try to install a Linux on a windows partition - some distributions accept that
Anyway, I suggest you have more than one partition in Windows (I have three partitions on my 80 GB WD drive)
Calin