The D5000 is not a professional camera, it's very much a low-end introductory consumer grade digital SLR aimed at first timers. It's a fine camera, but wouldn't last more than a few days at best in professional use.
The camera usually comes bundled with a "kit" lens, such as the 18-55mm. Like the camera, it's a cheap and cheerful model which is really intended just to get you started. It costs very little to make, and like the camera body it's not designed with longevity, servicing or repairs in mind.
But to answer your question, yes, you can buy the D5000 as a body only option without the kit lens and then add on whichever lens you prefer at extra cost. The 18-105mm has a longer zoom range so has more flexibility than the 18-55mm, but once again it's very much a consumer grade lens. You don't get anything for nothing, so in return for the additional zoom range in a lens which is of a similar grade to the kit lens you get poorer image quality and really noticeable barrel distortion at the wide angle (18mm) setting and pronounced pin cushion distortion at anywhere above around 24mm (click here
). You can't avoid these distortions entirely as all zooms are a compromise, but the kit lens suffers far less than the 18-105mm and also has a better all-round image quality (click here
). Again, not to professional standards, but more than adequate for almost all amateur users. To be fair, although the 18-105mm appears to be based on an older design and is totally unacceptable for any professional use, it also is perfectly adequate for most amateurs and is relatively good value at the comparatively low price it can be purchased for, but the Nikkor AF-S 55-200mm f/4-5.6 G ED DX is by far a better lens altogether and just happens to have very low image distortion across the zoom range. If you can get one, it's the ideal companion to the kit lens. Best of all, it's actually cheaper than the one you propose getting (click here
for comparison)and offers a much more useful telephoto range.
Please feel free to ask any questions if I've failed to answer your question in any way, otherwise, please take a moment to rate my answer.