[ShereKhan]

Carlos,

I'm sure that open office or even Word 95 is just as good.

If you are asking about basic licensing questions then i'm sure you are not going to be doing anything advanced.

Here's what versions of office exist (or existed)

Office 95
Office 97
Office 2000
Office 2003
Office 2007

I would put my money on 2003 or 2007.

Go to

Start > Control Panel > Add/Remove Programs

Then scroll down to Microsoft Office ... it'll show you what version you have.
Something like Microsoft Office Standard 2003.
There are lots of variants of office.

If you threw out your box with the hologram then you are screwed.
Normally the hologram should be on the CD packet for office.

The cost for a new bit of paper is anywhere in the region of £170+ depending upon variant of Office 2007 you want!