What is the best technology to develop an ERP/E-commerce?

Try SourceForge.net.  There are over 170,000 open source project to start your project with.  There are a million questions to ask about the fit, and there may be other projects that fit better.  However, there is a project as SourceForge.net called webERP that is written in PHP and uses MySQL.  I am one of the developers.  Inventory control is one of its many features but one that comes to mind that might be helpful is a link from a products photograph to the part number of the product.  This would allow one to create an ecommerce web site from data collected doing ERP.  webERP has EDI capabilities in case that is part of your ecommerce solution.  It is easy to integrate webERP with other web based projects.  

If you think you want to try webERP let me know by clicking my user id and you will see my web site.

It has multiple currency and language capabilities.  

As far as Linux, PHP and MySQL, those seem to be the most popular.  They are what I prefer for performance and they are easy to setup.

I have heard stories about .NET being faster to develop and easier to learn.  I have not found that to be the case in my limited .NET developement experience.  As and end user/ IT Manager, I find .NET a nightmare to keep running where my linux boxes just refuse to crash.

You can actually mix the .NET and PHP technologies with each page being one or the other.
If you find a project on SourceForge.Net that is web based using .NET and another that you with to integrate that is PHP, that should not be a problem.

Choose the database based on which projects to pick to integrate.  You can also mix databases but you waste some overhead if serving from one computer.

With webERP customers and suppliers can be allowed to login and see information pertaining to them.  Customers can enter their own orders.

Good Luck!

I just checked out osCommerce for the first time.  It looks awesome.  Since you get the source code with the software the answer is yes it can be integrated with any E-commerce where you get the source code. It appears to written in PHP 4 which is not easily integratable with PHP 5 (webERP).  The compatibility issues can be worked out.

I cannot imagine a more scalable piece of software.  It is web based using any OS platform, Novell, Linux, Windows and Mac.  Most web servers that will run PHP are able to be run in clusters.  Apache web server is well suited for clusters and load balancing.  MySQL can also be served by clusters of Linux servers and there are no license limits or fees ever and any of these products.  

I suppose compared to some of the more expensive software packages, open source is in its infancy but the model beats programmers in ivory towers already.  Support is more consistent, reliable, and cheap.  With hundreds of companies supporting most open source projects there is no chance of them "going out of business".  It is sort of like the old pioneer days where everyone helped build a barn or house.  Many people in the community have the skills.  Given the source code they can be local super experts for the software.  In the old days most packages were vertical meaning they were designed for one industry.  Over the years most have evolved to be horizontal and if they are feature rich then they are difficult to learn and use.

Open source is back to the vertical concept.  There are so many open source projects with no profit motive to merge that open source will be the best place to find vertical packages.

webERP has been downloaded over 160,000 times!