It appears that partitioning the hard disk for various operating system on the same hard disk can be confusing for some. May I offer a solution which no doubt is one of many available.

I have 3 op. sys. on one hard disk. i.e. winxp pro (fat32 file sys) suse9 (reiser file sys) and winxp pro (fat32 )

Use a Boot Manager to pick which operating sys. you want to use.
BootMagic7 fr PowerQuest is available for download at PCAnswers website

Install BootMagic7 in 1st winxp partition.
BootMagic need to be in installed in a primary partition formatted with Fat32 filesystem or it will not work.

I use PartitionMagic 7 to create all the partitions. PM7 does not resize partitions with reiser file sys. Be absolutely sure of the size of your reiser partitions.

A hard disk can accept a maximum of 4 primary partitions. To get round this, create 3 Primary partitions and an Extended Primary partition. Allocate as much disk space as you could for the extended partition.

In the Extended partition, create as many Logical Partitions as you want.

Most operarting systems have to be installed in the primary partition or it will not boot up.

Some op. sys. can be partly installed or wholely installed in a logical partition and can be booted up. You have to find this out yourselves.
eg. Suse, you can put the root in a primary partition and the rest like
Swap partition ,home or usr in a Logical partition. Install Grub or lilo in the boot partition. (i.e root )

In the Extended partition, Create Logical Partitions , eg label them :-
1."Data " to keep all your non sensitive files
2." Apps" to contain yr windows applications
3."Swap" for Linux swap partition
etc

"Data" partition need to be formatted with Fat32 file system so that it can be accessed by all the operating systems.

Sensitive data can be kept either in the original op.sys. partition
or in a Logical partition with the same file system as the op. sys.
eg, Win XP ntfs file sys.

The purpose of partitions is :-

a. to enable you to reload the operating system or format the partition, when it crashes without affecting your applications or valuable data

b. to enable you to back up all your valuable data easily to a removable media eg cd, cdrw or dvd. This is very very important as a hard disk failure will leave yr data unaccessible! Therefore get into a habit of backing up yr data regularly.

c. i. to separate yr applications software fr the op.sys.
ii. to reduce the op. sys. partition fr fragmentation, also reduce the time it takes to defrag the partition
iii. to easily find yr applications sofwares. Most sharewares will work without reloading

Finally, any helpful comments fr the forum community will be appreciated.