Had a bit more of a hunt about the 2Gb limit.
From a memory supplier.
Canon EOS 20D
Canon EOS 20D Memory Cards (Compact Flash) & Accessories
The following memory cards are compatible with your Canon EOS 20D Every memory card we offer is manufactured to the highest standard and carries a 2 year minimum warranty.Your Canon EOS 20D accepts Compact Flash cards.The largest
Compact Flash card you can use in your Canon EOS 20D is 2GB