First of all, you will need apps that can read these files and into which they can be saved. Pages will accept your Word docs and Keynote will take your PowerPoint docs. Once you have these apps, you can either email yourself the docs and choose to save them in Pages or Keynote from the email, which is handy for the odd one or two files. For a larger number, I would go through iTunes. Once you have these apps installed, you'll see them in iTunes under the app tab. When you scroll down, you'll see a list of apps that allow file sharing through iTunes. It is pretty self-explanatory have to transfer files to your iPad once you get to that point, but it is a question of finding the files on your comp then syncing your iPad to complete the transfer.
I think you can also put them in to the iCloud on your computer and take them off from there but I've not done that myself yet.
Here's some info i've just found on the Apple website:
Documents in the Cloud. And on your Mac or PC.
iCloud makes it easy to move Pages, Keynote and Numbers documents between your computer and your iOS devices. Just sign in to icloud.com/iwork in any modern web browser, and all your iWork for iOS documents will be there — complete with your most recent edits. Click a document to download it in iWork ’09, Microsoft Office or PDF format. You can also drag and drop any iWork ’09 or Microsoft Office document from your computer into one of the the iWork apps on icloud.com, and it automatically appears on all your iOS devices, ready for you to review, edit or present.
From this, I take it that you can transfer files to your iPad from your pc ( but you have to have the iWorks apps installed, eg, Pages, if you want to save Word docs), without going through iTunes, by using the iCloud site. I believe these docs take up space in your free iCloud storage allowance, so you may choose to buy more space or not store them in the cloud once transferred.