Most ERP vendors claim to use Microsoft technology - so do you need to worry? Yes.
It takes a large development team man years to bring an ERP system to market.
There are many ERP products that use non-current technology such as Paradox, Centura, SQL Windows, GUPTA®, Progress®, or Fox-Pro®.
While the vendors have added smaller components developed in Microsoft technology to sit on top of these dated technologies.
Many ERP companies are claiming their products are already 100% .Net. This is a very misleading claim. Seradex is fully engaged in assessing future Microsoft Technology. We can report that as of 2004 the .NET platform is improving and Microsoft has overcome some significant issues with the .net platform. Microsoft is turning these issues around rapidly and the future for .net is very bright. It is just reaching the point that Seradex can begin deploying in enterprise development.
So how do you tell what technology platforms ERP products use?
Here is a list of some ERP solutions and their platforms :

BusinessVision - Cobol

Coss - FoxPro

Made2Manage - FoxPro

Oracle - Oracle’s Proprietary Tools

PeopleSoft - Proprietary Language

Visual Manufacturing - Gupta

SAP - Proprietary Language - ABAP
To determine the technology platform of an ERP software product you can do several things :

Check the Internet search engines for product information

Go to the ERP vendors web site - check the job postings - what kind of developer skills are needed

Ask the vendor to supply a list of all files that are installed and all run time licenses that will be deployed

If the vendor offers a source code option ask what development tools are required