how to join two field together i have a content type named product. i need to add product like this:

title: product1

description: this is a product

company:a 
price:100

company:b
price:200

company is a node reference field with numbered of values set to unlimited and price is a text field but i don't know how relate price field with company.

if i can't do something like this in drupal 6, drupal 7 help me?
If you use CCK ver 3.x you get the multigroup submοdule. This allows you to create a group of fields like in you case company and price and then create multiple instances of this group. 

UPDATE

CCK ver 3.x is alpha. However I have used it in production without problems. You could look into the issue queue for bugs in the 3.x version before you use it. 

If you are creating a new site I would suggest going with drupal 7. CCK has moved to core in drupal 7 but the functionality of multigroup does not exist. 
However you can achieve a similar result using the Field Collection module. Looking at this http://oliverdavies.co.uk/blog/2011/08/create-multigroups-drupal-7-using-field-collections or this http://mostrey.be/creating-multigroup-widgets-drupal-7 will find out how.