First of all: Hello Aleksandr, welcome to Slackware!
Second of all: disks 3 and 4 contain the source code, not packages, so you may have problems installing that using pkgtool (read: it won't work!)
Thirdly:
Have a look at Chapter 18 of the SlackBook (I don't know why I don't recommend this more!), it might help you out in the long run: [urlhttp://www.slackbook.org/html/package-management.html[/url]
In the short term, try installing packages from disks 1 and 2 using:
Code:
installpkg /path/to/mypackage.tgz
Good luck and enjoy Slackware =)
- Piete.