IT really is quite amazing the lengths the private bankers of this town will go to keep their customers - especially the female ones - satisfied. News has just reached Keeping Posted of a highly classified dinner (everyone, but everyone, connected with it was sworn to secrecy) held at a five-star hotel where a select tai tai circle of Creditanstalt clients were entertained to a lavish dinner and given the opportunity to ''play'' with almost $500 million worth of jewellery. The exquisite pieces were loaned to the bank for the night by internationally renowned auctioneers, Christie's, who were displaying the collection in Hongkong, Tokyo and Singapore before taking it on to New York for auction next month. We were told that the 16 tai tais present were chosen because it was nothing for them to put their hands in their husband's pockets and fork out $1 million for a necklace. Some of the dinner guests seen playing with the pricey rocks and baubles like gleeful schoolgirls are regular fodder in the social columns (we respect their right to a bit of playful indulgence so we won't name them). But while the women preened themselves in front of the mirrors provided, and shrieked and wowed in delight, the same couldn't be said of their husbands watching nervously from a corner of the private room. They were resigned to knocking back stiff G & Ts and offering up quiet prayers that their spouses didn't form an attachment to any of the jewellery. All in all it was amiable fun, although there was a hint of niggling when the women came to choose which particular pieces they would wear while sitting down to dinner. The women weren't the only ones enjoying the diamond-encrusted regalia. Apparently, one of the bankers present also yielded to temptation and flirted with a diamond tiara. But we think our informant was stretching it a bit when suggesting that the gentleman in question bore an uncanny resemblance to banker-about-town Paul Giles. Such was the civility of the exclusive affair, that when it all ended, none of the departing guests was even frisked by the burly ex-Scotland Yard minder keeping watch by the door.