How do I improve Windows Subversion client update performance?

How do I improve Subversion client update performance? It appears to be disk bound on the client.

Details:

• CollabNet Windows client version 1.6.2 (r37639)
• Windows XP SP2
• 3 GB RAM with PF Usage around 1 GB and System Cache of 1.1 GB.
• Disk has write caching enabled
• Update takes 7-15 minutes (when very little to update).
• Checkout has 36,083 directories/files (from svn list)
• Repository has 58,750 revisions.
• Checkout takes about 2.7 GB
• Perf monitor shows % Disk Write time stays near 90% during update.
• Max Disk Read Bytes/sec got up to 12.8M and write got up to 5.2M
• CPU, paging file usage, and network usage are all low.
• Watching the server performance seems to show that it isn't a bottleneck.

I'm especially interested in answers besides getting a faster disk (especially configuration changes).

Updates from some of the suggestions:

• I need the whole thing so sparse directories won't work.
• Another client (TortoiseSVN) takes 7 minutes also
• TortoiseSVN icon overlays have be configured so they don't cause the problem.
• Anti-virus is configured to to skip that directory is it isn't causing the problem.