Actually, you have several questions stated or implied in your post.
First, if in fact you want/need real-time online interaction between your iPad and some central server (for example, to validate data being entered against a central database), you would indeed need either a wireless connection or 3G.
If you don't need a real-time online interaction, then you have several routes to go (but Access is NOT one of them, at least not on your iPad, since there is no "Access-capable" app for the iPad). celliott147's suggestion to use Filemaker on both your iPad and your desktop is a good one. But there's also a much simpler and less expensive solution as well.
Just create an Excel spreadsheet on the iPad using one of the apps that does so (Documents to Go, Quick Office, or Office2 HD). Capture your data into the Excel spreadsheet, and then import the file to your desktop where you have your existing Access database. Access itself allows you to import Excel spreadsheets, so you can update your Access database this way. Good luck.