I'd second Gerhard's suggestion - use a larger GIF size (like GIF733), and perhaps in your HTML code resize it to the size that you want.

SAS could have alleviated this problem by providing a **GIF RESOLUTION** value in their drivers, so that you could make your own GIF driver with the same dimensions but higher resolution... but it seems like they didn't bother (unless they've recently added this feature in 8.0 - I haven't looked yet).

So, I've done similar things to get nice graphs to include in a MS Word or Power Point document -- use a huge graph, and resize it in the document that you're working in.