Thank you for your post.
From your initial post, I don't know why it is running slowly. First, I would update to FileMaker Pro 10.0v3. You can download the updater from:
Next, open a database file LOCALLY and see if it takes a long time to load. If it seems normal, then try accessing the remote file. If this takes a long time to oopen, ask the person hosting the file to host another file and see if you can open that second file quickly. This will let me know if it is file related or network related.
In case there is some sort of port conflict on your machine, try quitting all other applications so only FileMaker Pro is loaded. Now, open the file remotely. Any change?
Are there any opening scripts with the original file? If so, what does the script do?
Try moving your machine to a different place on the network. That is, switch your machine with another machine that is working quickly on the network. Any change?
Any additional information you can provide may be helpful in narrowing down the possible causes.
I've encountered major delays getting a file to open when I have a "bad" external file reference. These references can list multiple locations for Filemaker to use in attempting to locate a file and it can take filemaker quite a while in some circumstances to determine that a reference isn't going to work and then move down to the next file path in the list. You might want to check for such issues by selecting Manage | External Datasources... and taking a look at each reference.