I have what looks like attempts to get to the c:\winnt drive of my server

... am I right to assume these are hack attempts? If so, can anyone point me to a URL where i can learn more about these types of events?
Additionally, there are now attempts to connect on port 25 to sites such as yahoo and MSN, are these attempts to bounce eMail?
Can anyone suggest how I can easily check that they were unsuccessful in their attempts?
(or point out to me that I am incorrect)?
Bron