You can't directly ignore folders on a checkout, but you can use sparse checkouts in svn 1.5. For example:
$ svn co http://subversion/project/trunk my_checkout --depth immediates
This will check files and directories from your project trunk into 'my_checkout', but not recurse into those directories. Eg:
$ cd my_checkout && ls
bar/ baz foo xyzzy/
Then to get the contents of 'bar' down:
$ cd bar && svn update --set-depth infinity
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