You could try this version of Rpm2tgz. It converts to a plain tarball, and then you can install the tarball:
I have been searching like mad in order to get Alien installed on Slack 10.2. All of the sources I am finding refer to installing it on Slack 7 and earlier. Does anyone know if Alien can be installed on Slack 10.2, OR does someone know of a tool to convert RPMs to tgz's? I have some RPMs that I NEED in order to get my RAID monitoring to work on this backup server, and rpm2tgz or rpm2targz didn't create all of the files when it did it's conversion. This is my luck... finally get WOL to work, build the kernel module for the RAID card from source and it works, but something as simple as the monitoring software can't be installed... Geez...
Asus A8V Deluxe Mobo
AMD Athlon64 X2 4400 -939
2GB Crucial DDR3200 Dual-Channel
ATi AiW 9800 Pro 128DDR
Sony DRU-810 DVD+RW DL
3 x Maxtor MaxLine SATA 160Gb 16Mb Cache
1 x Maxtor MaxLine SATA 300Gb 16Mb Cache
1 x Maxtor MaxLine SATA 120Gb 16Mb Cache
Also, Slackware provides a package called rpm2targz, that builds a Slackware package out of a rpm. Then, you can install it with installpkg.