hey if uve jailbroken it successfully..u shud see a Blue icon on ur springboard (desktop), sayin Installer under it. u need to have WIFI activated..
go into Installer, and it'll say that it's Refreshing Sources..then u have to go to the Install Tab (in the app), and then choose wat applications u want to install..just clikc on the application u want..and click Install on the right-hand corner up.
good source to get the mail, maps etc applications from the january update is to add applerepo.com to sources and going back to install tab and installing them