Are there any problems using headlights from a 2000 4runner in a 1997?

nope. easy swap. you'll have clear glass lenses rather than "frosted" glass lenses to boot.

No problems. Enjoy your vastly upgraded headlights after the swap! Per @MTD, the 99+ use reflector optics to shape the light versus the Fresnel lenses that the earlier versions used, thus the vast difference in performance and appearance. Your brights should be *ahem* a LOT better.

No issues, it's a great upgrade.

If you are looking at buying new, Rockauto has a great price on TYC headlights, when I bought mine there were just under $80 for the pair. Put in a set of high-wattage halogens (60W+, avoid the blue lights) and you'l actually have decent headlights that compare to normal cars!

I did exactly that on my '97. It definitely improves the lighting, and the look is much cleaner.

Having said that, my lights still felt somewhat dim (I should be clear, I installed junkyard '00 lights, not brand new ones). So I frequently used my HID foglights to augment the headlights.

Then I upgraded the bulbs to OEDRO LEDs, and the light output improved tremendously. So much so, that I don't even see the HID foglights when I turn them on in addition to the headlights.

So that's a very good setup, IMO.

is fresnel the technical term for the fluting on the lenses? Learn something new every day

No. Fresnel lenses always are composed of concentric rings or ridges. Lenticularly fluted would most accurately describe the old headlight lens style.
More info:
Fresnel lens - Wikipedia

Looks like you're right. Since I have a 99 I don't spend a lot of time staring at the earlier version headlights, however this link: Upgrade ’96 – ’98 Toyota 4Runner Headlights – Josh's World has a decent write-up of what OPs doing and has some good comparison photos.

Were your TYC 99+ headlight assemblies with glass lens? And were they not any more flimsy than the OEM units? I ask because there is conflicting info on the web.

I have not seen TYC headlights for the 4Runner, but I've use TYC lights for other vehicles, and while they were good from the standpoint of major components (housing, lens), their hardware always was inferior to OEM. And all the other aftermarket headlights I saw for the 4Runner had the same issue.

When I spoke to Daniel Stern about headlights for the 4Runner, he said the first thing he'd recommend is to get brand new Toyota headlights. Yes they are very expensive, but his point was that after 20 years, the surface of a used reflector becomes oxidizes and dusty, reducing reflectivity (and thus light output) tremendously. And he said to get OEM because none of the aftermarket brands have reflectors shaped as well as OEM.

Yes, it does have a glass lens which is clear and bright. However, I have had issues with one of the lights that I eventually replaced (just outside of warranty). There's a ball joint like coupler that keeps one side of the light fixed for the adjustment spring and it popped out and I couldn't get it to stay in.

The OEM reflector does have a slightly better beam pattern. I've got a "hot spot" in the lower left section of the driver's side light, but it's not anything terrible. For what you get, being a fraction of the price of a new OEM unit, it's worth it. I could buy 4 of these lights for the same price as 1 OEM headlight assembly.

Alas, It appears that Toyota USA sold out of all the newer, cool-design 99+ OEM headlight assemblies some time ago. They still have the pre-99 ones, however, which is what I went with.
To Mr. Stern's point, I noticed that the brand new OEM pre-99 headlight I installed was easily twice as bright as the 21-year-old OEM unit remaining on the truck, using identical bulbs. I see that the 99+ units are almost $400 from Amayama.

Good to know...thx.

I see quite a few 99+ headlights online for under $200 brand new. Like this - 81170-35300 - Genuine Toyota UNIT ASSY, HEADLAMP, LH

My original thinking was that for that kind of money, I'd rather do an HID retrofit. But since I'm not crazy about the looks of HID retrofits, I might end up going for the new OEM headlights.

Yeah, $320+ for a set of OEM headlights is rediculous. That's why the TYC headlights are an attractive alternative. I could do a whole lot of other things with $320.