Playing with SSIS I normally have to read flat files that come in zip format. The standard procedure here is to launch winzip, decompress the file, read it with a flat file adapter and then delete the uncompressed file. This behaviour generates a lot of useless I/O on temporary disks to decompress a file that will be soon deleted.
Another way of solving the problem is to have a look at DotNetZip library. A very smart programmer wrote a library that makes opening zip files very easy using .NET. He also added in version 1.6 a great function: OpenReader. You can open a zip file, look into its entries and open a stream reader on it.
Using this tecnique you can open a stream reader directly into the zip file and the process the stream using a VB source component in your data flow package.
And... Yes, you cannot use the flat file adapter. You will need to parse the stream and read strings from it but you will end up with very few I/O when compared to the unzip / read / delete solution. As I/Os are very expensive, this tecnique may speed up your package significantly.