First of all, a computer named win2k8fs1 does not have a PTR record - only IPs have PTR records.
If the current situation is:
wink28fs1.your.domain. IN A 192.168.1.1
192.168.1.1 IN PTR win2kfs1.your.domain.
then adding a second A record for that IP will work just fine.
Distinct A and PTR records only come into play when the connecting host checks the existence and values of both the A and PTR records, for instance on mail servers.
EDITed for better question:
As far as DNS is concerned, sure, every A record can have a corresponding PTR record.
That does not mean you should want to do this, however, as not all services using DNS will utilize the same method of choosing which record to use.
When the same label has multiple RRs for the same resource type, DNS returns all records to the client; which one the client uses is outside the scope of DNS.
This is not an issue (mostly) with A records, as you may want to, for example, host multiple web sites on one IP:
server1 IN A 188.8.131.52
server2 IN A 184.108.40.206
This is perfectly valid and results in the client connecting to the same IP for both hostnames.
However, due to the way DNS usually resolves names to IPs, the same is not true for PTR records:
220.127.116.11 IN PTR server1
18.104.22.168 IN PTR server2
This will, depending on what the client does, not yield the same result for IP -> hostname resolution as it will for hostname -> IP resolution.
As I mentioned earlier, not a problem for services that don't care about this sort of thing.