"Will a Nikon 105mm F2.5 AIS manual focus lens work on a Nikon D300?"
Yes it will.
However, in line with the subject of your post, the 105mm f/2.5 AIS is not a macro lens. You can always use extension tubes to make any lens focus closer than normal, but this lens does not have the near-field correction that is built into a macro lens and it won't perform up to the level of the 105mm macro (in Nikon-speak "micro") lenses on closeup subjects. Would it be good enough? Maybe - that depends entirely on how much you expect of your images.
Like others mentioned, the 105 2.5 AIS is not a macro lens (more a portrait lens from what i understand), but like Scotty's pic it can take great shots! (nice pic Scotty).
An alternative is either a used 105mm Micro (ie macro) Nikon, or look for a 60mm Micro (what i have). Some great deals out there if you hunt around a bit. Obviously there are also Tokina, Sigma, etc. macro lenses out there for a great price if you look. Quite a few are "macro" lenses (extra feature, as an afterthought), so might work depending what kind of macro you are trying to do?
Do you have a macro focus rail? Extension tubes? And are you looking to do ultra closeups greater than 1:1?
Rob, I do not have a maacro focus rail which I do want. I do have extension tubes and a Canon 500D that I can add to the nikon 18-200 and nikon 70-300. Closups 1:1 is sufficient most of the time and many things are ok as closeups. I am considering trying to rent a Nikon 105mm manual focus. I do have an older Sigma 28-200mm with macro capabilities and a Promaster 105mm macro but feel that I need a better lens. Recently, I have been using the Canon addition and extension tubes with good results, but I guess I am looking for better. Anne