>Hi all,
> Can I have vfp5 and vfp6 in the same NT4 machine?

Yes; the registry will have multiple entries, at least one distinct ProgID for each version. The version-independent ProgID will be claimed by the latest version of VFP installed on the given machine; not the most current version, but the version installed most recently, or at least registered most recently on the target system.

>Does it cause any problem? Anything I should be aware of
>before I install both versions in the same machine?

VisualFoxPro.Application for version 6 will work with both VFP5 and VFP6 programs; the VFP5 version (visualFoxPro.Application.5 or Visual.FoxPro.Application.5) doesn't know how to deal with FXPs compiled by VFP6. As mentioned, the last version installed will own the version-independent ProgID, and DBC whose stored procedures were compiled under VFP6 won't be usable under VFP5 unless the stored procedures are recompiled under VFP5. Stored Procedures in a .DBC compiled under VFP5 will be usable by both versions.