The easiest way to do this is via DTS (Data Transformation Service). Create a new DTS package on the SQL Server and follow the wizard to setup the source (Oracle DB) and destination (SQL Server) tables.

After you create the DTS package and test that it works, you can schedule the package to run every so often.

Here's some info on setting up DTS:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dtssql/dts_tools_wiz_8vsj.asp

Here's info on scheduling DTS packages:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dtssql/dts_pkgmng_4hm6.asp