This is my first post on this group...
Hopefully I can help out some...
I think it is possible to get a good vocal sound with a large Diaphragm mic in a small room.
If you use cardiod and face the rejection pattern of the mic, at the noise source (say computer) then it is suprising how clean you can get the mic.
Especially if at mixdown time, you utilise mutes etc, gating/expansion, and if you have it, even better ...noise profiling...that can get rid of virtually all the noise for you.
I record my vocals without headphones on, so I have my monitors, up just enough for me to hear and sing against. I face the back of the mic at the monitors and go from there.....
On my website is a mp3 snippet and the vocals on that were recorded in that fashion.
What I am getting at is, the amount of volume I have coming from the monitors far outweighs any fan noise in the room. Ok, yes, its not ideal but its certainly do ablem.
Also to if you use some sort of absorbative material , say a doona, rigid fibreglass wrapped in cloth, something, moving blankets work good, you can make a little area to record vocals in , that will work a beauty.
In fact doing some cheap treatments acoustically speaking, to your room, might just pay bigger sonic dividends than purchasing another more expensive mic than what you might own...
the mic used in the mp3 on my website is the Studio Projects C3.
cheers
Wiz