The MBR has only 4 slots for partitions. If you only would use primary
partitions you can have maximum 4 of these.
You also can have a single extended partition, combined with 0 to 3
primary partitions. You cannot have multiple extended partitions.
If you need to run Linux, it would be best to create 2 logical
partitions within the extended partition for Linux. One logical for
the Linux system and the other for Linxu swap. That would free up the
current primary ReiserFS.partition.
While Linux can boot from a logical partitions inside an extended one,
the BSDs only can boot from a primary partition. So besides Linux you
could install 3 other operating systems that need a primary partition.
A possible complication would be a "suspend-to-RAM" partition which
possible would take away one, only leaving you with only 2 primaries.
I never owned a laptop, nor did I use suspend-to-RAM so I leave that
issue to others ;)
=Adriaan=