For an one-dimensional standard Wiener process $W_t$, find $P_t(u)=P(|W(s)|\leq u,0\leq s\leq t)$.
This arises from the problem to find the first time a random walk has travelled a given distance, or the first time a $M/M/1$ queue grows up to a given size.
Maybe this problem is closely related to the Rice's formula?