It really isn't a surprise that architect Peter Cook was seen having a manicure this week. His claws were being sharpened for his divorce trial with model Christie Brinkley. Mr. Cook, he who was the architect of his marriage's demise by having an affair with an 18 year old, apparently didn't fully realize how much he would lose as a result of his wandering weenie. Life with Brinkley included beautiful homes, a glamorous social life, boats, first-class plane rides and the access his wife's success provided. And then poof, it was all gone when she threw him out. And naturally, he missed it. Having been married three times before marrying Peter Cook, Christie Brinkley obviously insisted on a pre-nup. Like many well-heeled people, she thought her lawyers had written a solid agreement. With her previous husband, musician Billy Joel, the divorce was dissolved amicably and both maintained their own incomes and self-respect. Then came developer Rick Taubman, whom she reportedly paid $1 million for freedom and sole custody of their son, Jack Paris, now 13. Having been financially burned by her relationship with Taubman, Brinkley understandably was insistent that the pre-nup with Cook would be ironclad. "Unfortunately the word ironclad is a bit of a myth," says divorce lawyer Clifford M. Solomon, partner of Solomon Tanenbaum in Westchester. "Anyone can challenge a pre-nup. And it has worked in some cases. Someone will challenge that the per ...