It depends. Bin is used by a number of different applications for different
purposes. What's in the .bin file you want to open, and what do you want to
do with it? Bin usually means "binary", which really isnt' binary at all.
Rather, it's come to me a file that makes sense to your computer, but not to
you. I.e., bin files usually don't contain plain text. If you open such a
file with a text editor and then close it, you will invariably loose all of
the non-text characters, making the file unusable for its original purpose.
So, when/if you open such a file with an editor of some kind, it's generally
best to make a copy of it rather than opening it directly.
If you just want to look at it, you might make a copy and then try using
either WordPad (for large files) or Notepad (for smaller files). There are
some binary editors out there, but I've lost track of what they are in
Windows XP. There also are various programs designed to display "binary"
files. You might Google "binary editor" or "binary display" and see what you
come up with.