Elek Drums is a Groove Agent One expansion. GA One isn’t included in Cubase LE 5.
But you’re in luck, you can upgrade to Cubase AI 8 for a super low price. AI 8 comes with Groove Agent SE 4 which has new content along with all old Groove Agent One kits, and it can load your Elek Drums expansion.
For details see here: https://www.steinberg.net/nc/en/support/knowledgebase_new/show_details/kb_show/cubase-ai-8-cubase-le-8-update-offer.html
After upgrading, you can then to upgrade to Cubase Elements 8 for € 49.99 if you want. With Elements you’ll get much more freedom, more effects, a light virtual analog synthesizer and the Acoustic Agent studio kit for Groove Agent SE 4, which is far more realistic and flexible than the other stock GA SE4 kits.