|i want to connect to computers with a straight through cable|
You can't, it has to be a crossover cable.
Now anybody know how to check that my nic supports Auto-MDIX?
I don't need to check, I already know your NIC doesn't support auto MDIX. But feel free to google the make/model of your NIC's and read the spec sheets on them.
You know, a crossover cable is pretty cheap. I suspect you could get a 15 foot (5 m) cable for like $5 to $10. Call a few local computer and electronics stores and see what they sell them for in the length you need.
With regard to your sharing a folder, what you want to do is on the "target PC" (ie: the one with the share you'll be connecting to remotely) is to create a user account for the PC connecting to the share. When creating the user account, use the exact same username and password used to logon to that computer at bootup. Add the user account to the share and grant appropriate permissions.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.