DreamHost does not offer a reseller account as such, but you are free to resell your hosting at any price you see fit.
You can offer your clients either FTP/Shell access only, or give them limited access to the panel using WEBIDs and privileges. The privileges you can grant are explained in the wiki article linked below;
Note that you can not 'brand' the panel, so your clients will always know that they are being hosting by DreamHost. If this is a problem, then perhaps DreamHost is not the best solution for you.
Edit: How odd, the post I was replying to seems to have vanished before I could finish writing my reply. :s
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