Another on avrfreaks is OSPII - open source programmer. It’s written in an odd dialect of freeware BASIC that translates to a wierd open source C compiler. The BASIC code for this is a line by line translation of the Atmel C++ version.
About the only VB6 code I’ve seen is what I uploaded as BLIPS to avrfreaks called BLIPS. It is a bootloader, not an ISP. It’s intended to be a fast/good way to update the flash/eeprom using the serial port and a connection by cable, wireless, LAN, Internet, etc. You use an ISP once to install the bootloader AVR-side code (included with BLIPS). BLIPS is a PC side program (GUI based) to load the flash and eeprom of most any AVR chip including the mega128’s. It’s written in VB6. The AVR-side code is written in asm to be small; it’s 512bytes including code for fast block mode downloads. I uploaded the asm source; the VB6 source isn’t uploaded but I’m flexible.