HOW good is Singin' In The Rain (Pearl, 2.00pm)? It is a question you will be able to ask yourselves many times this afternoon when you are confined to your armchair, thanks to the vagaries of Hong Kong's worst summer. It is very likely the greatest musical MGM or anyone else ever produced. Singin' In The Rain has everything - great songs, great dances, a nostalgic story and a fine cast, led by Gene Kelly, Jean Hagen and Debbie Reynolds. It even has milk. The famous scene in which Kelly sings the title song (which first appeared in Hollywood Revue Of 1929) was shot time and time again because the rain looked as weak as water. Eventually a bright spark on the set hit on the idea of mixing the water with milk, to make it stand out more on camera. Other trivialities include the fact that the Broadway Ballet scene took one month to rehearse, two weeks to shoot and cost US$600,000, a big pot of money in 1952, even for Hollywood. This scene is the one that includes a guest appearance by Cyd Charisse and her ''crazy veil'', a 25-foot piece of white China silk that streamed about her, kept afloat by three airplane motors whirring off-camera. The real history of Singin' In The Rain began when screenwriters Adolph Green and Betty Comden were asked to create a story that would tie together numbers from the best of MGM's musical output. They found that some of the finest of those tunes appeared in films made during the transition from silents to talkies and decided to focus their story on that dynamic period when new stars replaced old; when bright, shiny faces took the place of rouged vamps and mascaraed lotharios. The plot - as if it really matters - begins in 1927 and concerns dashing Don Lockwood (Kelly) and blonde bombshell Lina Lamont (Jean Hagen). They are one of Hollywood's favourite romantic teams, but Lina mistakenly believes their on-screen love is for real. NOTHING is for real in Double Impact (Pearl, 9.30pm), except some of the Hong Kong settings, and even most of those have been remodelled in the short time since this was released in 1991. Most surreal of all is Jean-Claude Van Damme's attempt to play two characters. They are identical twins separated at birth, one of whom grows up to be a gruff, cigar-chomper; the other a lighter and more charming individual. There is a slow-motion love scene worth watching for and the fact that Hong Kong provides the backdrop is of passing interest. THERE have been three films made called Time Bomb, but only one spells it Timebomb (World, 9.30pm), which is something of a claim to fame. When mysterious people try to kidnap watchmaker Michael Biehn he decides to find out why, so he kidnaps psychologist Patsy Kensit to help him. Timebomb is a decent blend of sci-fi and spy thriller. THE comedy High Season (Pearl, 12 midnight) must be mentioned because it stars Kenneth Branagh, who later became famous for marrying Emma Thompson and producing some above average movies himself. High Season is lightweight fluff, but it does offer stunning views of leading lady Jacqueline Bisset and Greek island settings. Trick Or Treat (Pearl, 1.40am) must be mentioned because it stars rock singer Ozzy Osbourne and also because it is not half as bad as it might have been. Osbourne is a dead star who is brought back to life when a fan plays his latest album backwards. THE French film Games Of Artifice (World, 12.25am) is said to be about androgyny. Scriptwriter Virginie Thevenet said she wrote it because when she was a child she wanted to be a boy, ''although now I am happy to be a girl''. THE documentary The Story Of Vinh (Star Plus, 2.30pm) tells of a young Amerasian making the transition from Vietnam to a new life in America. Vinh was one of thousands of Amerasians abandoned by their fathers in Vietnam at the end of the war. They encountered discrimination, hostility and mistreatment from both sides. Many were left by their mothers to fend for themselves on the streets because their faces bore the features of the enemy. Under intense pressure, the US began to repatriate Amerasians in the 80s. But for Vinh, as for many, the struggle to adjust was not an easy one.