I just got a six week old malti poo yesterday.  He was very playful and seemed in good health last night.  This morning I first noticed that he was breathing quite rapidly and hard.  He has vomitted one time and has diarreha.  I have not seen him eat a solid thing since I recieved him.  We have purina hi-protein (breeder advised), but the dog has yet to eat anything.  He will drink some water here and there.  You can just tell he doesn't feel good.  Please help. 

I think if your gut feeling is telling you he is not good then I would contact the vet better safe than sorry as 6 wks is very young to leave thier mother its usually 7-8 wks .
Puppies can become ill very quickly.

I would take him off to the vet, even when drinking OK a small puppy can quickly dehydrate with diarrhoea, is he insured?  6 weeks is very young for a toy puppy, infact toy breeders generally tend to keep puppies longer than average often 10-12 weeks, did you get him from a responsible breeder would you say, ie a member of a breed club breeding to their code of conduct from appropriately health screened parents?  Please register (its free :)) so you can answer these questions and we may be able to help you further.
PS I have just noticed this is a cross breed puppy (I thought it said Maltese reading it quickly :o) I would doubt very much it is from health tested parents and certainly would not be from a responsible breeder to be frank I would return it before you become too attached as not only is the probability of heartache increased you are encouraging another litter of cross breds to be bred.  I know that sounds a bit harsh but that is the only way to stop this sort of irresponsible breeding happening.

As it isn't a breed I would think not!!!

Take your pup to the vets straight away.  As the others have said a responsible toy breeder doesn't sell their pups until they are 10 weeks old, our Pom's go at 12 weeks.  Even my Spanish who are a medium size breed don't go until 7 weeks and they are retrieving toys at 3 weeks of age.

Hope all goes well with your puppy.  Join us and advise on how he's doing.

I can only echo what other posters have said.  Go to a vet immediately.  6 weeks is very young and puppies can go downhill at an alarming rate, so please seek help straight away.

Let us know how he does, fingers crossed for you.