OS Multiboot

what 3 distros are you concidering?
for complete newbies to linux, xandros, red hat and mandrake have the simplest install.
mandrake has a slightly better config with multiboot.

you will have to rebuild hdb ( slave drive ) partitions as ms partitons are useless for linux.

a good partiton structure, with lots of room for distro's yet simple to work with:
*Verbatim
partition mount point size
hdb1 / 5gigabytes
( root partition for first distro)
hdb2 /home 4 gigabytes
( first distro user's files )
hdb3 swap double system ram
( uses this instead of pagefile. )
hdb4 / 5gigabytes
( second distro )
hdb5 /home 4 gigabytes
hdb6 / 5 gigabytes
hdb7 /home 4 gigabytes

the partition numbers will be different.
but that is the structure.
the extra drive space can be allocated as:
hdb8 /mnt/transfer rest of space
this can be used to transfer files between distros without fighting with different config files for each distro.

the menuing system with each distro uses customised icons, so multiple ditros using same home directory will create conflicts with the look.

filesystem types. there are a number of options to be concidered.
ext3 and reiserfs are journalised, fast, and stable.

for the transfer partiton, use fat32, then you can downoad in linux, and access in windows, without a virus running before scanning the file.
I personally use ext2fs in my filesystems.
doesn't have the journalised features, but it's the old, tried and true file system

I think you try to install GRUB. It's a power full MultiBoot Loader.

it depend, linux can get all the partition from your hard drive and install it on a linux loader ( lilo) or grub loader.

the best thing i used is XOSL it install itself to the mbr and it will take all your partition and make a menu out of it.