Depends what you mean by "access linux".
Do you want to be able to login? Do you require command line access or X?
Here are a few suggestions.
Command Line
The most secure way of accessing linux to be able to run commands on the command line is using ssh. The ssh server will need to be installed on your Linux machine and you can then use one of several methods to login. The ssh web site is:
http://www.openssh.org/
SSH clients for Windows include:
GUI / X
There are some ways of accessing a graphical screen from Linux on a Windows Client. A common method is vnc.
Another way is to run a windows based X server and export your clients from Linux to display on your windows machine. I don't know of any free solutions to this but it is possible using Hummingbird's Exceed (I believe it's now been renamed to Hummingbird Connectivity).
Transferring Files
Or perhaps you just want to transfer files between Windows and Linux which can be achieved (as mentioned already) using ssh, or to setup Linux as though it was a Windows share using Samba
As you can see there are many different ways of "accessing" Linux depending upon what you are wanting to achieve. I suggest you take a look at some of the links above and decide what you are wanting to achieve.