Recently I was working on a project which needs to integrate Drupal + Salesforce + Ubercart + Webform. Thanks to our drupal community contributed modules due to which I was able to do the integration successfully.

But to have it done there are prerequisite which needs to be done which are required for the integration, so I thought of noting them here:

Make sure your have OpenSSL enabled for your PHP installation. For me on windows just needed to add, 'extension=php_openssl.dll' in my php.ini file and restart apache server. If this line is already in your php.ini file , just uncomment it.

Create account on https://ap1.salesforce.com

Create your Security token :
1. login to above account and got to :
Profile -> Setup > My Personal Information > Reset My Security Token. The token will be emailed to your email address. Make a note of the token key.
2. Create your wsdl ( Web Service Definition Language ), by going to your profile -> setup -> develop -> API -> API WSDL ( click on appropriate WSDL and save the file in a directory named wsdl outside your site root. eg: c://xampp/htdocs/wsdl ). ( i downloaded the enterprise wsdl xml file. )

download and enable salesforce module from drupal.org :

Download the Salesforce PHP Toolkit :
https://github.com/messageagency/salesforce
its actually soap client which needs to be placed in salesforce module within the "toolkit" directory in "salesforce_api".
You should end up with something like:
sites/all/modules/salesforce/salesforce_api/toolkit/soapclient

got o admin/settings/salesforce ->
1. In settings -> Salesforce API settings ->
Enter your username , password and the Security token generated.
for WSDL directory settings give the path of the wsdl directory created.

Now in Object Setup of Salesforce you can enable/disable the objects of salesforce available and configure those with fields by FiledMaps.
You can test the integration by going to Test/Demo and try exporting your user account as an contact in salesforce.
It will create a contact in you salseforce account. If its created then you can be sure that your integration is successful.

further integration with ubercart :

For mapping of Ubercart Orders form Drupal and Salesforce :
download and enable http://drupal.org/project/uc_salesforce module :
By default the Opportunity object from Salesforce is mapped with Ubercart Order.
In the readme.txt everything is properly given.

Hope this helps :)