Hello JPBoudreau,
Firstly, don't worry about the "potential Multi-user directory problem" as being related to slowness. This means that you have access multiple databases and initialized with different path indicators. Maybe due to the new server having a different mapped drive letter?
Adagio is a multi-user; multi-file application where data files can be quite large and are read and updated over the network. Accounting programs like Adagio will require more network power than using a program like MS Word that only opens a single file (by a single user) that typically will be quite small. This is why Andrew asked about the 100MBits/Sec access.
If you want to identify how much the network environment affects data access in Adagio, try making a copy of your data and put it somewhere on a local hard drive (rather than the network) and use Adagio to open the local copy. If you see a very significant difference (you will always see some difference) then some investigation into the network will be necessary (especially since you reported that other applications are also slow). Note that having the programs on the network will not have anywhere near the performance affect as compared to data access on the network.