I was looking for this info a couple of days ago and one of the first places google sent me was this thread but since I found the info and the thread still appears as a coogle source for it I thought I might as well post here the info to make it work.
First the font similar to the one used by the IBM 3270 terminal is called nouveau-ibmand can be downloaded from this link: http://www.dafont.com/nouveau-ibm.font
1) Download it, then install it by double clicking on the font and clicking on the install button.
2) Open PuTTY and load the site you want to use it one by selecting the site and clicking on load.
3) On the left pane select appearance and then select font and use the Nouveau IBM and set the size to 12
4) On the left pane select colours and select Default Foreground and change the values to: Red: 29, Green: 233 and Blue: 122 and then select Default Bold Foreground and change the values to: Red: 31, Green: 255 and Blue: 141
Once you login into your server you should be able to see the font like this: