Sigma 18-200mm vs Tamron 18-200mm lenses for Nikon D40x?

Are these good quality lenses? I just got the Nikon AF-S 55-200mm VR lenses,

http://www.bhphotovideo.com/...ikkor.html

and I'm thinking about returning it to get either one of these…

http://www.bhphotovideo.com/...II_DC.html

http://www.bhphotovideo.com/...Di_II.html

Are these lenses good? Are they better than the Nikon Lenses? And if yes, which one is better, Sigma or Tamron?

Added (1). And I was looking at this too,

http://www.bhphotovideo.com/...ED_VR.html

Is the Nikon D40 DSLR a respectable camera for someone beginning a Photography hobby?

Is the Nikon D40 DSLR a respectable camera for someone beginning a Photography hobby?

Auto focus messed up my manual focus?

Okay so i set my lens to autofocus to see how well it worked and i took a picture up close. But when i switched it back to manual, it won't focus on things that are far away, i can only focus on things that are close up. And when i used the autofocus to shoot something far away and put it on manual to shoot something close, i couldnt get it to focus. How could i fix this? I usually only use manual but after autofocus messed everything up i can't really use the manual setting anymore. I have a nikon d3100

I have Nikon D5100. I like to buy lens 18-200mm. Nikon lens is very costly?

Any third party lens is available to my D5100?

I want 18-200mm with auto focus.

Does a Nikkor 55-300mm AF-s focus faster on a d7000 than a d3100?

I was just wondering since the d7000 has an internal focusing motor and the d3100 does not, though I'm pretty sure it doesn't matter.

How would you interpret this venue's camera policy?

World's Oldest Rodeo is starting tomorrow. I live pretty close to the fairgrounds, and I was thinking that it would be fun to get tickets to one of the events so I could work on my action shots a bit. But on the ticket sales page, they have pop-up windows that say "No recorders or cameras with detachable telephoto lenses allowed."

Would you assume that they are referring to All DSLR's when they say that? The event tickets are nonrefundable, so I don't want to buy them and then find out that I can't bring my camera in at all. I have a Nikon D90 and the 18-105mm kit lens along with a 70-300mm… Obviously the 70-300mm is out of the question, but are they likely to consider the kit lens a telephoto?

And if they do consider that telephoto… Do you think they'd let me use masking tape to secure my lens to the camera body so it's no longer detachable? *trollface*

Added (1). If I had a shorter zoom lens, or a bridge model, I wouldn't be asking this question. :$

What cameras are similar to the Nikon D5000?

I'm looking in to purchasing an advanced camera and a friend of mine has the Nikon D5000. I'm open in looking into that camera or any similar styles. If you have any suggestions or advice, I would gladly appreciate it.

Nikon D3100 - Help (20 characters)?

I don't usually use liveview on my camera. But how come when i don't use live view i can't change the AF-area mode?

Mono MICROPHONE ON NIKON D3100?

Another question.
I ordered my NIKON D3100. I found out its mic is Mono? What does that mean? And can't we attach a better mic with it?

Does Nikon d3100 have electronic viewfinder?

Also what's your opinion on Nikon d3100? Your answer will settle my dilemma so that is whay i say to you thanks loads