If you have a low ID, make sure the XP built in firewall is turned off. To do this, right-click on My Network Places, select properties, right click on Local Area Connection, select properties, choose the advanced tab and then uncheck the box below.
emule xp firewall
If you are still getting a low ID make sure your software firewall is configured to allow eMule access. I recommend letting eMule have full access in your firewall settings. If you want to configure the individual ports, the default ports are:
4662: TCP incoming and outgoing
4672: UDP incoming and outgoing
4661: TCP outgoing
4665: UDP outgoing
4711: TCP incoming
Putting checks beside "Use smart LowID check on connect" and "Safe Connect" in Preferences>Server should help correct a low ID problem.
emule safe connect
Routers can also be the cause of a Low ID if you are not properly forwarding ports. eMule Router and Firewall Help has a detailed section on routers including Belkin, D-link, E-Tech, Siemens Speedstream and Zyxel 650HW. The Official FAQ also has info on routers.