IP Sniff - How Granular does it go?

Here is my predicament:
We have a client who is hell-bent on having the opening page within their site asking for the user to input their Zip Code to set cookies and send the user to the desired site pertaining to that area.

Example: Enter in zip code 90210 – Get redirected to stores in Hollywood etc…

Big problem: Organic Search engine optimization takes a real kick in the you-know-where when this is done because of the spider will not be able to go past the form asking for the Zip code.

I have been looking at switching out the form page and going with an IP sniff

Question: How granular does the IP sniff go (Country, State, District, and Town?)

Is there other ways of skinning this cat?

You don't necessarily need to go as far as identifying the IP address of the search engine spiders. They update their IP addresses very frequently, and it's difficult to keep up with them.

If a visitor won't accept the cookie then just feed them a page that doesn't include the form.

So I guess what I should be asking is how I can get the spiders past the form page (which the client is adamant about keeping) unless there is a 100% guaranteed option available

right now... the spiders will not pass

I was assuming that an IP sniff would be 100% but was curious on knowing how granular the sniff can go...

Probably the best term for it would be "IP Delivery". The only information you "get" is an IP address. You have to know the addresses of the search engine spiders and be able to feed them a page without the form--or don't require that they fill out the form.

Why not put the textbox up and also a "view all" text link that will let the spider in?

Oh my. Did the guy hire you for your search engine expertise?

If yes, then he should let you get on with the job.

If no, then you should walk away and let him screw his own site up.

You can use useragent sniffing server side to let in search bots, a lot of big sites do that, washingtonpost.com comes to mind.

But if google tests your site with a standard useragent, like msie, they'd be blocked, but that is an acceptable solution.

However, I agree with above, clueless clients can't be helped. I just dumped one for that reason.

One business problem that I can see is for travellers researching their destination city.

A traveller goes to the trouble of entering his Chicago zip code, but wants to see the best restaurants and theater locations for his Atlanta business trip.

The site is losing out on the multi-billion dollar travel market.

There has to be a work around for that problem which would also solve the complete indexing delima.