you can't find hdmi to vga adapters because hdmi is digital and vga is analog.
A vga monitor can NOT "interpret" digital. digital is just a sream of zeros and ones.
dvi is either digital, analog or integrated. Just having a hdmi to dvi adapter does not convert it to analog nor does a dvi to vga transfer it to analog. Those adapters are only talking about the pin/out.
You can use only ONE video output at a time. You can not use vga out at the same time as hdmi out. Some vostros came with video subsystems that could output to four monitors at the same time, but not all models had this feature and those had to be customized AT TIME OF PURCHASE ONLY. You did NOT have that capability built into the system you purchased. If you did, you would have all the outputs the same.
If you want twin (cloned) monitors you can use a Y adapter, but it is not good for either the vidcard/mobo OR the preamp inputs in the monitor if done more than a few hours a month. This will NOT give panoramic output.
vostro 3500 is an EXCELLENT entry level business class machine. It has superb reliability, and can be configured in a VERY broad range of ways. You did not tell us how you configured it, but agina multiple vid out was not even offered on that model. The3500 is NOT dells top of the line business computer. It is not a multimedia compute,r and it certainly is NOT a gaming computer. The TOP vid card you could configure that unit with, was only a 512 one live output nvidia, NOT the 4 output vid card available on other vostros, latitudes or precision workstations.