CS didn't overwrite 6 on my system. There EULA usually allows you to have both installed for "transition", so that you can use plugins that have compatibility issues or import into applications that are confused by the new version. There is no formal definition of the transition period. You are allowed two installations, as long as only one is in use at any time (but there is no actual check on that). Unlike the MS system with OFffic, which I gather insists that one be a desktop and one a laptop, Adobe allows for any mix (so you can have PSCS at home and at work). The timing is not clear, but as with MS activation the record will be purged after a while so that you would need to phone only if you used both installations within a limited period. The activation reportedly bases itself on the HD only, so changing video cards and such should not be a problem. Under XP, make a restore point after activating PSCS as it puts some of the key in the registry and a system restore could wipe it otherwise: however in that case you would be able to reactivate without using up a slot as the part on the HD's sector zero would still be present.