Using a ADSL SpeedStream 5200 Router.
*I opened (port forwarded) my 65500 tcp port to my ip, to work with azureus (torrents). someone can do something with this? is this making my pc vulnerable?
when i scan my 'modem ip' (192.168.254.254) with nmap, said tcp 21 (ftp) 23 (telnet) 80 (http) - 'open'.
how can i close them? and how to make a 'external scan' from here?

*sometimes a email comes saying that my message could not be delivered because of viruses! and friends receives messages from my mail without i send them! sadly, my sister is using my winbloze lately. people can send emails using my address, right?

I opened (port forwarded) my 65500 tcp port to my ip, to work with azureus (torrents). someone can do something with this? is this making my pc vulnerable?
Any computer connected to a network with outside access is vulnerable in some kind of fashion. The only true and secure machine is one not connected to anything but itself where only you have physical access to it.

when i scan my 'modem ip' (192.168.254.254) with nmap, said tcp 21 (ftp) 23 (telnet) 80 (http) - 'open'.
how can i close them? and how to make a 'external scan' from here?
Either turn off these services or setup a firewall to keep anything outside your network from using these services, ports, etc.
Make an external scan? Get a shell account or run a scan from another computer from outside of your network of course.

sometimes a email comes saying that my message could not be delivered because of viruses! and friends receives messages from my mail without i send them! sadly, my sister is using my winbloze lately. people can send emails using my address, right?
Get virus protection for Windows and tell your sister to stop opening unwanted mail she doesn't know who the sender is. Be careful in what you download.