Firstly, the DALnet server pools are not always open, and if they they usually only have 1/2 servers linked to them. Make sure you connect to a server that is as close to your geographical location as possible (for example, if you live in the USA, then you would try finding a .us server). You can find a list of servers for DALnet, here
It would be useful to know about exactly what message you're getting. If you know that you are not responding to server IdentD requests, then you must have connected at some point - If you are getting AKilled for IdentD problems, then view this page
(look at that for general IdentD problems too). If you have Windows XP (Home or Pro) then make sure the Internet Connection Firewall isn't on.Start > Control Panel > Network Connections
Right click on the connection you're currently using (the one you use to connect to DALnet anyway) and then click on Properties
- Go to the Advanced
tab and if the box is checked, uncheck it.
As for firewall ports, make sure you have at least ports 6667-7000 open, and for IdentD port 113.
As for other IRC connection errors, see this post