How do I get my dad to ingest food and liquids?

Hello,My dad was just recently diagnosed with Non-Hodgkin's Lymphoma. The doctors have told us that the cancer is not in any of his organs or bone marrow, but is a tumor mass pressing on his stomach. He is 81 and was not eating very much for about a month before this was detected 3 weeks ago. As a result he is weak and unable to receive the heavy duty chemotherapy that the Sloan-Kettering doctors at the Denville, N.J. unit would normally recommend for him. Instead for the past two weeks they have given him two treatments of Rotuxin, in the hope that the aggressive tumor may be halted or perhaps slightly diminished in size, thus allowing my dad to eat and drink more so that he can build up his strength for the more demanding chemotherapy (which he has told the doctors he wants to receive). He has two more weeks of his Rotuxin treatment remaining. Throughout the last two weeks we have tried a variety of approaches to get my dad to eat and drink, but our efforts have produced only minimal results. My dad claims that he has a hard time swallowing (even though all examinations by the encologists and other physicians have indicated that there should be no problems in doing so). He also says that he feels he is going to vomit when he trys to eat anything, even though he has not done so when he does eat a little. Can anyone give us some suggestions as to how we can help our dad eat and drink more, so he can build up his strength and get him over what we know is just the first hurdle?