Ok, you have three choices:
1) Pay somebody to do it, I don't know where you'd go or how much it would cost but I'm sure an online search would bear fruit. If there's only a few cassettes to convert this may prove the preferable option.
2) Buy a DVD recorder that also copies cassettes to DVD, this is probably the easiest but most expensive option.
3) Do it yourself using an interface device between the VHS recorder and your computer.
An example:
Terratec video capture
And this is the one I use, it works well but only with XP or Vista 32 Bit OS's
Dazzle
You will also need software, the first example I've given comes with suitable software and my Dazzle came with Pinnnacle Studio Lite which does the job.
You will need at least a 2Ghz dual processor and lots of hard disk space for temporary storage, 500Gb - 1Tb of free space should suffice.
With video capture, conversion and editing the more powerful the processor and the more memory you have the better.