Cant access site intermittently, site not available

My answer to this question has a run-down of propagation time that I'll link to instead of copying+pasting here.

More specifically from your question it sounds to me like you authoritative name servers have not been updated (or are listed wrong so the wrong ones are being queried). To see what name server records your local DNS servers thing are being used for the domain you can use the dig <domain.tld> NS like so:

$ dig spillett.net NS
;; ANSWER SECTION:
spillett.net.           316     IN      NS      ns1.nogoodnamesareleft.com.
spillett.net.           316     IN      NS      ns2.nogoodnamesareleft.com.

you can then check them to see if they all have the right address for the name:

$ dig @ns1.nogoodnamesareleft.com www.spillett.net
;; ANSWER SECTION:
www.spillett.net.       349     IN      CNAME   spillett.net.
spillett.net.           349     IN      A       69.94.124.51
;; AUTHORITY SECTION:
spillett.net.           349     IN      NS      ns2.nogoodnamesareleft.com.
spillett.net.           349     IN      NS      ns1.nogoodnamesareleft.com.
;; ADDITIONAL SECTION:
ns1.nogoodnamesareleft.com. 3499 IN     A       69.94.124.137
ns2.nogoodnamesareleft.com. 3499 IN     A       78.105.118.25

(repeat the above for each NS record returned by your first query)

The TTL values returned by the queries directly against your domain's nameservers should always be the actual value set in the zone record (they are low in the example above as that domain was moved around recently and I forgot to set them back up higher when I'd finished), where-as for queries against non-authoritative servers (i.e. one of your default local name servers, which will be queried if dig is not given an @<server> directive) will be how long before that server next checks (against the nameservers listed as NS records for the domain) if its cached version needs to be updated.

Checking the above tests for your domain may give you some more clues as to where the source of the issue lies. If you are using Linux and don't have dig, it is usually found in a package called something like dnsutils (it is called that on Debian ad Ubuntu, I assume a similar arrangement on other distributions) - there are no doubt many ports to Windows (this is the first relevant looking page returned by Google) though I've never used any of them myself.

I believe nslookup is used to test a DNS server itself, as opposed to utilizing your HOSTS file. http://support.microsoft.com/kb/200525 seems to indicate as much.

Try just a simple ping. Does ping myMachine.MyDnsSuffix resolve to the loopback address you have specified in your HOSTS file?