I have this lens and all I can say is WOW! For the price it can't be beat. Sharpness, color, and contrast are super. I think you can get it online for about $325-350 range. Check it out. You won't be disappointed.
I do not have a D100 but have shot this on my F100 only.
I have had this lens for a couple of years now - like it a lot actually. Use it on my F90X and on borrowed D1 and D100. Works great, good sharpness, colour etc. BUT I am probably going to trade it for the Nikkor 105 macro - simply because it is the only non Nikkor in my bag and it looks out of place
I bought the 180mm HSM last summer and used it for butterflies and honey bees, etc. I was so pleased with the results- I wish I could up load, but no scanner. If it's "bugs" you're after, this one would about double your range. I think you could find it on the web for under 600 US. Pricey, a little, but I plan on keeping this till it falls apart.
If that 180 EX is built anything like my 3 EX's it will last longer than you will. hahaha I have done some real in justice to my 28-70 EX and it just keeps working. I did have to send it in after a little accident in Cabo May 2002. After I whacked it had against the roll bar of a jeep it wouldn't focus to the minimum focus any longer. And when I say I whacked it hard I mean hard I thought it was broke. I shattered my Nikkor 105 MF with less impact.
I sent the thing into Sigma usa and they fixed it. No charge, even though it was my fault and out of warranty.
I have it for my F80 and F100 and I'm impressed. AF is a bit slow closeup maybe, but you'd mostly use manual focussing then anyway (and the AF does work).
Compared it on camera with the Nikkor 60mm Micro and liked the feel of the Sigma better. Doesn't weigh as much yet feels more solid, that and the longer focal length sold me on it (before going into the store it was my second choice after the Nikkor).
any size is fullframe for a given definition of frame