Since it is a D5000 it isn't a full frame camera? So it would still be a 35mm?
No. On the D5000 it would act like 35mm x 1.5 = 52.5mm. That's not a wide angle lens. For what it's worth, I wouldn't consider 35mm on a full-frame camera wide either.
To the OP: You should think about what and how you plan to shoot and then decide on whether you want a wide-angle lens or a telephoto that goes longer than your current one. Shooting with a wide-angle can be a lot of fun, but it is difficult to compose interesting shots. If you like to shoot architecture, then it is a good choice. It can work well for certain landscape shots as well. Other than that, you have to get pretty creative to make your photos look interesting. It can be done, and to great effect, but it is more difficult.
For what it's worth, I have the Sigma 10-20 and I like it a lot.