defragging won't make any noticeable speed difference until the drive gets to around 75% full
To be truthfull, I quite like it when people try defragging drives on older machines, because often the extra extended workout will push any older tired drives (i.e. anything over three years old) over the edge. By defragging an older drive you run a very high chance of killing it
As to the registry, best to leave alone unless you are cleaning up after a malware infection. Vista / Win7 loads the registry in such a way that the "dead" parts of the registry don't get loaded.
Again theres a downside in running these registry cleanup programs - most are incapable of analysing the Microsoft .NET runtime files and often delete things that shouldn't be. Microsoft report this as one of the commonest user-caused software errors. Leave alone unless you really know what you are doing