Question about Trend Micro Internet Security 2007 license

I'm about to purchase Trend Micro Internet Security 2007.
But I'm confused whether to buy the 1-user license or 3-user license
version.
I have 2 computers at home that I use myself (one for work and the
other for personal use).
Both are connected via a router to the cable broadband.
Can anyone please tell me if there are any constraints or limitations
(e.g. ability to download virus updates)
if I install the 1-user license on the two computers?

Thanks in advance.
Andrew