Some den isn't it. Try this for logic:
1) Laptops usually cost much more than Desktops so is a laptop really necessary
a) it has to travel ? - laptop
b) it must not eat space ? - desktop under table, with keyboard and LCD screen need same space as a laptop ! the printer needs the most space !!!
c) it must live a long time ? - only Desktops upgrade easily, if at all - so lifecycle is 3+ years if you buy a 'top of the line' specification today.
2) Like the logic of quality is cheaper... often true, but with the electronic devils I'm not convinced - what you probably want is "good & quick service" when it decides it doesn't want to.
Refer to 1a above - will that be limited to home or on the road as well ?
3) Screen you defined 15" - would suggest if you save by taking a Desktop, then up the size to 17, 18 or even 19" LCD - if you spend more than an hour or so at a PC session its kinder to your eyes, especially as even you will not get any younger, modem (needed to communicate) V90 is the spec at 56.6Kbps.- its virtually standard, Disk space .... 30Gb is fairly standard - 20Gb is probably enough, unless you want to write a book or store all your photos or video's digitally and on-line; if that's the case the bigger the better within your price range. Removeable storage - a DVD and CD reader and writer are the current coming standard (the DVD writer bit solves the photo's and video film problems). Memory - depends on the operating system you will run - 256Kb is OK, 512Kb is mor than enough today and should be fine for 3-4 years. Which operating system ??? well if its a Mac... then theirs... and if its Windows... suggest that W2000 is enough and that you don't need XP.. but in 3-4 years time...it will probably be the only thing around.
(XP has the disadvantage that Bill asks you to register and he knows about more of your private life than its worth.). Do NOT construe that to be saying that you should try to avoid paying for software - that is NOT what I said.
4) If you want cheap office software (Text, Spreadsheet, Slide Presentation only) then Star office is great value for money, but it is not everybody's taste. Many machines come with that from IBM/Lotus or even from Microsoft - and that can be a price differentiator.
Get a Firewall if you are going to be on-line to the web a lot (especially if its a broadband connection - fast but...needs a firewall). Also get antivirus software - there are good free ones available but you might just want to go for the Symantic firewall and Anti-Virus solution and pay for it.
5) The comment about highstreet stores not understanding what they sell is mostly true, in the UK there is a company TINY that seems to know what its all about however. DELL, Compaq (now HP), IBM, Toshiba, Sony, etc. all have their fans and haters so you can often discount the comments (have had all 5 in my time and for me the most important is service time and ease of using the keyboard and tools. (I hate joysticks, but that's just me).
Finally - discount all of our comments, and find a trusted friend who has a compter that works reliably and doesn't need permananet fiddleing with (for preference one who lives nearby and will continue to do so and who will bail you out for a beer when needed).
Good luck, G
ps if you have the answers, feel free to mail me - on condition that if you follow any advice, its your fault not mine.