Well, it "is" what it "is", so I'm not sure what you mean by that question.
Yes. It will not, however, work properly till you make some adjustments as phpAdsNew uses register_long_arrays (see earlier post in this thread where Simon addresses this issue.)
You can install almost any script you like (with certain restrictions per Dreamhost's TOS), including phpAdsNew, though for some to run correctly (or at all) you may have to modify the script(s), or the change which version of pre-installed PHP you run on your domain, or install your own version of PHP, or modify the installed PHP's settings via the use of your own PHP.ini file, etc. as described in this Wiki article.
Another approach you can take is to run phpAdsNew from a fully-hosted sub-domain (as in ads.yourname.tld, etc) where you set the sub-domain up to run PHP4. Good Luck!