pc5

HI, I have 5 PC's in our firm. It was previously all qin 98. Now I upgraded pc5 and pc 3 wiht win xp. Now the problem which i am facing with networking. That ic an access pc which having win 98, i.e, pc1, pc2, pc4. But when i try to access PC3 and PC5 it ask for password. what may be the...