I wanna know how to host wiki pages say on geocities or some place else..

I don't think the free sites give you enough access to be able to support such a site. You need to be able to host and use CGI scripts/programs in order to create such a site. I don't know of any free hosts that give you that.

I wanna know how to host wiki pages say on geocities or some place else..

There are some smaller freehosting sites that allow you to use php, however, Geocities and most other free homepages dont allow you to have php pages, or other sever side processed pages saved by you. However most allow javascript, so there still can be a solution.
It is quite long and complex though.

Javascript in turn can create http connections after the html page is loaded (see AJAX, or IFRAME-RPC). This is pretty much all you need.

The solution wuold be to use javascript to make http connections to an existing application that can store your wiki pages. This is anything on the internet that you can access by authenticating yourself via http, and retrieve/save information. Also, only you should have access.

Examples are email accounts, private message boards, group pages such as msn groups which you keep private, private google groups etc.

Using a free email account as an example:

Im not sure if you can use javascript to authenticate yourself on a pop3 or IMAP server, though this would make it simpler, but you can definately use javascript to authenticate yourself on a webmail page, like yahoo, gmail, hotmail, or the open source horde, or squirrelmail.
(you can also send emails from javascript, but i think that will create a popup telling the user you are sending an email)

To authenticate yourself, you will make a http post request to the webmail account using javascript. The http post request will contain your username and password.
This will grant you a session to your webmail account from the browser that made the http post request.
(Your username and password will be visible on the html page making the request, but this can also be solved by having users register, and in registering they create their own free email accounts. They then use their own username and password).

Editing pages:
Once they are authenticated, they can edit pages, just by sending an email. (The email is sent by making the right http post request to the webmail account to send the email).
The email titles are the title of the page, and you can add a line to the body of the email that says, edited by 'whoever' at 'time' etc etc.

In essense all you are doing is using the already avaialble service on the web, but creating a different user interface, with javascript and html.

I think there isa few projects on sourceforge.net that make use of free hosting and other free stuff on the web to save data.
cant think of the names though.

Try searching the web for AJAX.
And also http post and http authentication.
Also, http post vulnerabilities, or form post vulnerabilities.

good luck. ;)