I would go with the 800 series. Cisco recommends SOHO for office up to only 5 users (home office).Here is a comparison for you.http://www.cisco.com/asiapac/channels/files/SOHO90_Cisco830_QA.pdfMK
Did you ever get to resolve this? I am having similar problem. The concentrator is at 3.5.5 IOS level and I am authenticating to an NT server. Everyone gets authenticated no matter whether they have dial-in permissions or not in NT.Thanks,Mike