Advantages:
16bit applications (many old programs are 21bit),
Can handle less RAM (if you count that as good),
There is a higher chance of there being a 32bit driver for slightly obscure devices than there is for 64bit drivers.
Disadvantages:
Less RAM,
No 64bit applications (I don't know of many 64bit exclusive apps anyway),
Less future proof.
Oli
My Computer
Computer Manufacturer/Model Number
Apple MacBook 5,1
OS
Windows 7 Profesional x86, Mac OS X 10.6 Snow Leopard
CPU
Intel Core 2 Duo 2.4Ghz
Memory
4GB DDR3
Graphics Card(s)
Nvidia 9400m
Monitor(s) Displays
13.3" Internal + 22" DVI + 21.5" USB
Screen Resolution
1280x800 + 1920x1080 + 1920x1080
Hard Drives
Internal SATA 2.5" 500GB (395GB Mac HFS+, 105GB Windows NTFS)
2.48TB RAID consisting of 5 disks (HFS+)