Lenin viewed racism as a product and a tool of bourgeois society. Racism is used to win over working-class people to sacrificing and dying for imperial adventures abroad (in Lenin's time, tzarist expansion in central and east Asia, in our time, wars in Afghanistan and Iraq), and also to divide different sections of workers (who would otherwise be the overwhelming majority) in their struggles for economic freedom and political power. Therefore, racism was definitely an obstacle to socialist revolution. The way to overcome these national rivalries was to build an "international" of socialists from all over the world. Delegates from China, India, and elsewhere came to the first congresses of Lenin's Third International (which would later betray 1st and 3rd world movements time and again after Lenin's death).

To see Lenin's views on the use of racism as a tool of imperialist policy, look up "national self-determination" vs "social chauvinism".

Domestically speaking, Lenin would advocate for labor-organizations in various nations to instill working-class consciousness and combat forms of "false-consciousness" that divided the working class, which include racism, sexism, homo-phobia, and religious divisions. He wrote letters to American revolutionaries convincing them to argue for the inclusion of blacks in the labor movement, and, were he around today, he would probably congratulate Egyptian Mulsims and Copts (Christians) for coming together at Tahrir Square, despite centuries of Muslim oppression toward Copts.

Racism is one of the issues that, Lenin would argue, necessitates the formation of a "vanguard-party" of the most class-conscious workers. Common economic oppression alone are not enough to get workers to unite, since racism divides and oppresses different sections of workers. Class unity can't be left to spontaneity... It takes organizations of trained and conscious anti-racists, anti-sexists, etc, to work amongst their co-workers, neighbors, and fellow soldiers, to win them to the idea of racial unity.

I thought that nice chap I quoted above explained it pretty well.

Know the game!