I'm looking for a list of the 5 biggest Halloween parties in Las Vegas
- on actual Halloween (Oct 31st). I need details on location, costume
style (naughty or normal), cost of entry, links to pre-purchase
tickets and expected number of attendees. Parties can be at the casino
nightclubs or independent venues. Please do not recycle last year's
party list - most of those aren't on again this year.

Some ideas:

A List of Las Vegas Events on Halloween 2006
http://vegas.napkinnights.com/events/index.php?d=2006-10-31

Red Rooster (WARNING: not for the timid or uninformed, read web site carefully)
http://www.vegasredrooster.com/halloween2006/index.html
This is a world famous annual Halloween Party. If you can handle it,
this is a party you will NOT forget.

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Nightmare on 54th Street 
Studio 54 
MGM Grand 
3799 S. Las Vegas Blvd. 
Las Vegas , NV 89109 
OCt. 27- 28, 2006 - The show starts at 10pm and from what I hear it
should include some very appealing costumes. Like always a costume
contest will be held with cash prizes.

40th annual Beaux Arts Ball
When: Oct. 31, 2006
Where: Studio 54 at MGM Grand
Tickets: $20 in advance, $25 at the door

Well man you said youu need information about the 5 biggest halloween
events in Las Vegas, i think this can help you:

1- In this site u can find a list of halloween events with information
about place, costume requirements, adress and how to get in contact
with them

http://govegas.about.com/cs/nightlife/a/halloween.htm 

2- here you have information from a travels agency with information of
eventes for the halloween weekend in las vegas, in the web you can
pre-order tickets to varios parties and shows (the page is in spanish
with an english option)

http://espanol.vegas.com/halloween/index.html

3- This one have information for kids hallowen events with contact
information and prices.

http://www.lasvegaskids.net/las_vegas_halloween/halloween_events.htm

4- Need a costume for halloween? look at this

http://lasvegas.citysearch.com/roundup/38068

5- Information about the VEGOOSE, An outdoor music festival with giant
grimacing jack-o'-lanterns and a hodgepodge of superstar, indie and
up-and-coming bands.

http://www.lasvegasvegas.com/2006/06/vegoose_returns_for_halloween.php

and how to pre-order tickets for VEGOOSE (with a list of artist)

http://shop.vegas.com/shows/showtimes2.jsp?event_id=15375&lang=es

I hope here u can find what u need, and please excuse me bad english.