Hi purplelotus! Of course, you can be in relationship with whomever you want, no one in the poly community needs to approve you or stamp your hand for access to our world, LOL.
We have a member here, Sage, who blogs specifically about her experiences as a mono in relationship with someone who is poly. You might want to start with her oldest entries first, so you can see how she adjusted, shifted her views with new discoveries, and struggled with certain issues. She also wrote an e-book for monos. If you visit her blog, you can order one (it seems that the link she has on the right-hand column is the correct one for ordering). Here is the link: http://polyamorouspeople.typepad.com/polyamorous-people
There are also some Yahoo groups for people in poly-mono relationships. I know one of them is here: http://groups.yahoo.com/group/PolyMono/
But feel free to ask away! There are a few monos in poly-mono relationships here.