There is a known issue in URL Rewrite Module 1.0 release related to the importing of mod_rewrite rules that use rewrite conditions with REQUEST_URI server variables, for example:
RewriteCond %{REQUEST_URI} /some/url/path.ext
ReweriteRule .* - [L]
Such rules may not work correctly after being imported to IIS.
Please upgrade to URL Rewrite Module v1.1 which has a fix for this issue.