right now, im not using any kind of routers or firewall, just my cable modem direct to my pc.
Look your modem up in http://www.portforward.com/english/routers/port_forwarding/routerindex.htm.
If it's in there it has a router built in, so you'll have to forward ports in it. Follow the link, choose mIRC DCC - IRC DCC
and follow the directions.
im using port 1024-5000 right now!
So mIRC will be using all those ports - it's a huge range. How many simultaneous chats and sends are you planning on doing? 10 is usually more than enough. Just pick 10 sequential numbers between 1024 and 5000 - it's best to pick a starting point at random, in case someone wants to use those open ports for an exploit. Make him work to guess the range you picked.
do i have to use port 10051-10070 in my mIRC options --> Advanced
You have to use a small range of ports somewhere between 1024 and 5000.