Hi,
It is difficult to help not knowing what you have done, there is no clue from a simple page not found error. Possibly the files are not uploaded to the correct root folder. Possibly your site is not configured for ASP.NET.
To be honest, while I do recommend 1and1 for dedicated servers I have only ever heard bad things about their shared hosting.
mojoPortal requires ASP.NET 3.5 SP1
probably 1and1 shared hosting also requires medium trust configuration as most shared hosting does.
Hope it helps,
Joe