My 540i is on the original chain guide and tensioner. There's no abnormal sound at start up so I'll leave them alone until otherwise.
Make sure to have a PPI on that X5. Have your parents budget for a cooling system overhaul and suspension overhaul if they haven't got done already.
Good luck.

please elaborate, I'd really like to hear how the service work you've done on one of these BMW engines compares to a simpler, older engine

looking at the timing chain guide replacement procedure from the bentley manual seems pretty straightforward, but what I'm worried about the most is how difficult it is to get to things in the engine bay, i would expect alot more components to have to remove

thats great, it seems like alot of people are saying that! whats a PPI, an inspection?

ill look into the suspension and cooling costs, thanks!

You can't be serious with this question.

To elaborate on this would take weeks. About the only thing that's the same between a BMW M62 and an older, simpler engine is that they have spark plugs, pistons, a crank and run with a mixture of fuel, air and spark.

You can say just about everything else is totally different and far more complicated.

what service procedures have you done and in your opinion based on the work you've done on a BMW engine, what aspects of the service are going to be significantly different?

its great you guys all work on these engines and can provide some insight as far as what to expect, so what parts of service would be significantly different and why? im so used to people on forums just making up stuff they dont know anything about and have no experience with, this is so refreshing

how well do the bentley procedures match the real world procedures?

PPI = Pre Purchase Inspection
Have it done at a reputable BMW Independent Shop. It's like a bill of health of the car in question. You can base your negotiation on the report too.

Best way to know about the condition of the guides is to remove the valve covers and look.

Many BMW DIYer on this forum as well as other forums had screwed up when it comes to timing an engine with the vanos system. Just google problems with engine after vanos rebuild.

Get all the proper timing tools for the rebuild, then follow the instructions, take your time and clean everything as you take it apart. Don't go into this project thinking you can get it done over a weekend having never delved into an M62 before. I'd say allow yourself at least a couple of weeks, then if you do get it done over a weekend or week, you'll be overjoyed!
Once you get things like the radiator and engine wiring harness out of the way, there is almost enough room to climb in there. Be glad you don't have a 540, those suck for room.

as far as the differences between an old chrysler 4 cylinder and a bmw v8? everything. I've never worked on a chrysler though. But Chevy, Honda, VW, Toyota and BMW, I have. 70's Chevy is the easiest to work on, followed by my 89 GMC/Chevy also being simple and easy to work on. BMW is next as generally the most logical and well laid out, but maybe that is because I'm an engineer and the way BMW does things makes sense from an engineering point of view. Honda is next. Then I think Toyota and VW have different teams design different parts of the engine, then ask a kid how they would connect the parts together and do it that way.

Lots of threads on here for the guides and tips for doing it. Read all of those. Then go on the E39 and E38 sites and read their guides. Be aware that the M62 in the X5 is different than the e39 and e38 because our CCV is on the back of the engine and their CCV is inside the front timing cover.

racingbmwm3 has hit the nail on the head.

As a person who has dug pretty far into working on two different M54 engines, I have to agree that, overall, these BMWs are some of the easiest and most logical FUEL INJECTED engines that I have ever had to work on. And doing a suspension job and brake job on this car was about half as difficult as it was to do it on my older Focus, and even easier than my 1990s Mustang and my old Ram truck. Fords from the era of my Focus were a mixed bag of SAE, Metric, Torx, and tamperproof hardware that required a huge rollaway toolbox to have enough to get the work done, plus the different engineering teams that had to make different components work together, just like racingbmwm3 was talking about with Toyotas.

On my BMWs, all I need is a metric wrench set, a metric socket set with Torx, a rubber mallet, some screwdrivers, a pliers set, and I can get just about anything that I need to do finished with minimal cursing and minimal bleeding. Just get yourself a good manual set (sounds like you have the Bentley, so that's a great place to start), stay active on the forums, and just about everything will be within your reach if you are remotely mechanically inclined.