When I was configuring IIS on my 32 bits small instance, it asked me for the windows installation files (i386). You can attach these to your image as an EBS (Elastic Block Storage) volume.

• In your AWS Management Console navigate to “Volumes”
• Create a new volume and give it a minimum size of 2 GB
• Be sure that is in the same Availability Zone as your instance
• Then enter a snap-id for me it was: snap-a4bb5ecd, but here is a list of other Snapshots:
  Windows 2003 R2 Enterprise 32-bit: snap-a4bb5ecd
  Windows 2003 R2 Datacenter 32-bit: snap-b8bb5ed1
  Windows 2003 R2 Enterprise 64-bit: snap-a6bb5ecf
  Windows 2003 R2 Datacenter 64-bit: snap-babb5ed3