Data connectivity with SAP is done usually via RFC directly from the machine you are working on. You can write simple VBA scripts that connect to R/3 via RFC. There is a set of DLL on your Windows machine that is installed along with SAPGUI; this is the proxy bridge to SAP.
To upload data, you only need an RFC enabled function in SAP that receives the data for you.
Alternatively, you can write a small BSP page in SAP and send data via HTTP; that way, you will not need anything installed on the client.
Click here for a very old document of mine that describes in detail how it works.
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