dhacker is correct (I completely forgot about this - never used it so far - at home I will calculate if it would make sence for me to "buy"/exchange 5'000 miles to get 10'000 HHonors points and may be then to get the nov-99-Hawaiian holidays on Hilton-award-basis (I have, so far, only about 30'000 HHonors-points on my account).
Rudi, I do not know whether your Diners Club is having this promotion or not, but here in the US there are two promotions with Diners Club Rewards points:
1) Double miles to Delta on Feb 1999.
2) 50% bonus for HHonors sometime in spring 99.
Rather than transfer United miles to HHonors, I suggest looking at Diner Club points for the transfer. Here in the US best would be to transfer Club Reward points to Delta, and then transfer Delta to HHonors.
thank you Pankaj, unfortunately it is not possible. Diners Switzerland let's me only get Swissair (ratio 2 points = 1 mile), UA-miles (terrible bad ratio 4 points = 1 mile) or BA (I don't even now the ratio, because, till now, I converse the points only to Swissair/Qualiflyer).
In Switzerland Diners had a double points promotion from nov-15 to dec-31st-98 (but the points-rate is worse then in US, normally it is only 1 point per 2 Swiss Franks, and one Swiss Frank is about US$ -.70, during promotion it was 1Sfr = 1 point).