Thanks James for your input, but could you please elaborate your point of view more ?
Also, I want to clarify my question by giving an example, which is as follows:
Here is a web part for MOSS 2007, assume that I have reused the same source code, then I packaged the solution using SharePoint Solution Installer. Now I have a deployable package of a web part for MOSS 2007.
I want the same web part for SP 2010? How?
At the moment, I am creating another solution, and using different packager tool.
So, my question is how to have one web part that could work on both MOSS 2007 and SP 2010 ?
BTW, there is another crucial issue which is related to supporting Multilanguage. Assume that I want my web part to support English, German and French. So, basically I will use resource files (.resx), that means: for the MOSS 2007 WP I will deploy these resource files in
..\12\TEMPLATE\LAYOUTS.., BUT for SP 2010, there’s 14 Folder.
Therefore, how to tackle these issues, and create one single web part that works on both MOSS 2007 and SP 2010?