Upgrading Drupal

how to update the drupal modules when site is online

Please I may need to know if it could be possible to upgrade a Drupal site from 5.1 to latest 6.x with all the modules listed below. I did not do the site myself so I do not know all these modules how are configured but I know that the webdesigner that did it used them all to gave us a rich and useful portal.
I've tried to follow the update tutorial and one of the first step is to first update the modules.
I've done that by Upgrade Status (I get tons of update alerts) and downloading the latest version of all modules.
I've done that, uploaded to test server all the folders of updated modules.

When I try to re-open the drupal 5.1 site it crashes for date module. I've tried to delete this (deleted its folder) and then it crashes (error = Fatal error: Call to undefined function token_get_values() in **/modules/page_title/page_title.module ).
Trying to delete page title module I get again another error for next module.

So my question is:
Is it possible to upgrade such a site and keep its functionalities or it's very complicated?
How should I proceed?

thanks in advantage for kind help

Here there is the list of 70 used modules:

actions
aggregator
availability
block
blog
blogapi
book
calendar
cck
checkbox_validate
color
comment
contact
contemplate
content_taxonomy
date
drupal
event
faq
filter
forum
globalredirect
gsitemap
help
image

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http://deepubalan.com/blog/2010/02/08/common-questions-of-a-drupal-begin...

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